CVE-2023-40267 - How An Incomplete Fix in GitPython Opened the Door for Command Injection (with Demo)

Git is everywhere—from open-source projects to enterprise releases. So, libraries like GitPython make working with Git nicer in Python programs. But sometimes, a small oversight in security can blow up later.

Let’s break down CVE-2023-40267, a story of a fix that didn’t quite fix enough—and how that left a crack open for attackers.

What Is CVE-2023-40267?

In August 2023, a security issue was found in GitPython, a Python library widely used to work with Git repositories programmatically. The bug (tracked as CVE-2023-40267) affects versions before 3.1.32.

The Problem in Simple Words:
GitPython didn’t properly block some unsafe options when you used clone() or clone_from(). Attackers could sneak in malicious arguments, triggering nasty side effects like code execution. This happened because a previous fix for CVE-2022-24439 left an incomplete patch!

Backstory: The Previous Fix

In CVE-2022-24439, attackers could inject dangerous options into the clone commands through "non-multi" arguments—settings not meant to be used more than once. The GitPython maintainers tried to put a patch in place. But the fix only blocked a subset of insecure arguments, and didn’t account for all the ways user input could sneak past filters.

Let’s look at a simplified vulnerable code flow in GitPython < 3.1.32

from git import Repo

# Suppose this input is from a user (e.g. an API call)
repo_url = "https://example.com/repo.git";
clone_path = "/tmp/safe/path"
options = ["--config", "core.sshCommand=ssh -o ProxyCommand='malicious.sh'"]  # Not safe!

repo = Repo.clone_from(repo_url, clone_path, multi_options=options)

multi_options is supposed to be a whitelist for safe, repeatable options.

- But if the filtering is incomplete, a user can send unsafe things like --config core.sshCommand=…—which can run shell commands when cloning.

Here’s a more "evil" example that could be used to demonstrate the vulnerability

import os
from git import Repo

os.makedirs("/tmp/evil", exist_ok=True)

# Malicious payload pretending to be a config option
malicious_opts = [
    '--config', 'core.sshCommand=ssh -o ProxyCommand=sh -c "touch /tmp/yougotowned"'
]

Repo.clone_from(
    'git@github.com:someuser/safe.git',  # Or any accessible repo
    '/tmp/evil/repo',
    multi_options=malicious_opts  # This might have been allowed in vulnerable versions!
)

Remote Code Execution (RCE): Attackers can run arbitrary shell commands.

2. Triggered via User Input: If your Python app allows users to control clone options (maybe via a web form or API), you’re at risk.
3. Incomplete Filtering: The fix for CVE-2022-24439 missed some cases, so GitPython before 3.1.32 was still vulnerable.

Who’s Affected?

- Any app or script using GitPython < 3.1.32, especially if it allows user-provided options for cloning.
- Cloud CI/CD platforms, data science notebooks, and web apps that integrate Git functionality.

How to Fix It

Update immediately:
Upgrade to GitPython 3.1.32 or later. This closes the loophole for insecure "non-multi" options.

pip install --upgrade gitpython

Don’t trust user options:
Never let external user input become command-line options without strict validation.

Extra reading

- Official CVE-2023-40267 on NVD
- GitPython Security Advisories
- Release notes for 3.1.32

Lessons Learned

- Partial fixes = future headaches: If a security patch doesn’t fully close the hole, attackers will find a way.

Filters are hard: Blocking dangerous options is tricky—test as many angles as you can.

- Least privilege always: Limit what features you expose in your code, especially when dealing with subprocesses or system commands.

Automate security testing for your codebase.

Stay safe and keep your Python projects secure!
If you enjoyed this deep dive, share with your dev friends—or check your own code for these hidden traps before attackers do.

Timeline

Published on: 08/11/2023 07:15:00 UTC
Last modified on: 08/25/2023 03:15:00 UTC