GitPython: Remote.pull() arbitrary command execution via refspec injection

GitPython's Remote.pull() method contains a vulnerability in its security guard intended to prevent command injection. While the library attempts to block dangerous options like --upload-pack, the guard only inspects keyword arguments and fails to validate the positional refspec argument. An attacker can supply a refspec starting with --upload-pack=, which is forwarded to the underlying git pull process. Because git pull does not properly terminate positional arguments before passing them to internal git fetch operations, the injected command is executed as the upload-pack program. Exploitation is possible when using local filesystem or SSH transports. No fix is currently available.

Attack Chain

1. Exposure: An application calls Remote.pull(refspec=<value>) where <value> is derived from attacker-influenced input.
2. Control: The attacker provides a string such as --upload-pack=<command>; git-upload-pack.
3. Path: The input passes through Git._unpack_args and Git.check_unsafe_protocols without being flagged as malicious.
4. Guard: The unsafe-option guard incorrectly assumes positionals are safe, failing to check the refspec against unsafe_git_pull_options.
5. Primitive: The refspec is passed to git pull -v -- <remote> <refspec>.
6. Execution: The git pull command forwards the positional to an internal git fetch without a -- separator, causing the system to execute the injected command as the upload-pack program.
7. Result: Arbitrary command execution occurs on the system with the privileges of the calling process.

Impact

Successful exploitation allows arbitrary command execution as the user running the GitPython process. This requires the use of SSH or local filesystem transports; HTTPS transports are not affected as the server ignores the client-supplied upload-pack program.

Recommendation

• Validate that all refspec strings passed to Remote.pull() do not start with a hyphen (-).
• Prefer HTTPS remotes over local-path or SSH transports where possible.
• Avoid passing untrusted user input directly into GitPython method arguments.
• Monitor for GitPython processes spawning child processes that are not standard git utilities or that originate from unexpected command-line arguments.