GitPython unsafe clone option gate bypass through joined short options

GitPython version 3.1.50 blocks unsafe git clone options such as --upload-pack, -u, --config, and -c unless callers explicitly pass allow_unsafe_options=True. However, the default unsafe-option gate does not recognize joined short-option forms such as -u/path/to/helper.

Git itself accepts -u<upload-pack> as the short form of --upload-pack=<upload-pack>. As a result, Repo.clone_from(..., multi_options=["-u<helper>"], allow_unsafe_options=False) can execute the helper command even though the equivalent long option is blocked.

Affected package:

• Ecosystem: PyPI
• Package: GitPython
• Confirmed affected version: 3.1.50
• Repository: gitpython-developers/GitPython
• Current PyPI version during triage: 3.1.50

Relevant behavior:

• Repo.unsafe_git_clone_options correctly lists --upload-pack, -u, --config, and -c as unsafe clone options.
• Repo._clone() splits multi_options with shlex.split(" ".join(multi_options)) and then calls Git.check_unsafe_options(...).
• _canonicalize_option_name("-u/path/to/helper") returns a string beginning with u..., not the canonical short option u, so it does not match the blocked -u entry.
• Git accepts the same joined short option as --upload-pack=<helper> and executes the helper during clone.

Preconditions:

An application must pass attacker-influenced clone options into Repo.clone_from(..., multi_options=...) while relying on GitPython's default unsafe-option gate to block command-executing options.

The local PoC uses only a local bare Git repository and a local helper script. It does not contact any third-party service.

Local reproduction:

The PoC creates a disposable bare Git repository, a helper script, and a sentinel file path. It first confirms that the long --upload-pack=<helper> form is blocked by GitPython. It then calls Repo.clone_from(..., multi_options=["-u<helper>"], allow_unsafe_options=False).

Observed sanitized output:

gitpython_version=3.1.50
git_version=git version 2.53.0.windows.1
tmp_dir=<tmp>
long_upload_pack_gate=BLOCKED:UnsafeOptionError
joined_short_upload_pack_gate=ALLOWED
clone_result=EXPECTED_EXCEPTION:GitCommandError
sentinel_exists=True
sentinel_text=GITPYTHON_UNSAFE_OPTION_BYPASS

The clone fails because the helper exits nonzero, but the sentinel file proves that Git executed the helper despite allow_unsafe_options=False.

Impact:

An attacker who controls multi_options can bypass GitPython's default allow_unsafe_options=False protection and execute a local command via Git's --upload-pack / -u clone option. This is a residual bypass of an explicit GitPython security boundary, not merely a case where a caller opted into unsafe behavior.

Duplicate / related advisory checks:

• OSV query for PyPI/GitPython version 3.1.50 returned no vulnerabilities.
• The repository's public advisories include related unsafe Git option issues, including GHSA-x2qx-6953-8485 / CVE-2026-42284 and GHSA-rpm5-65cw-6hj4 / CVE-2026-42215. Their public affected ranges are marked as fixed before 3.1.50.
• GHSA-x2qx-6953-8485 describes validating multi_options before shlex.split(...). GitPython 3.1.50 now validates after splitting, but the joined short option -u<value> still bypasses because the validator canonicalizes it to u<value> rather than u.
• GHSA-rpm5-65cw-6hj4 describes unsafe underscored kwargs such as upload_pack=.... The current PoC uses multi_options=["-u<helper>"] against 3.1.50 and does not depend on underscored kwargs.
• GitHub issue search for upload-pack unsafe options found historical related items, including CVE-2022-24439 and the earlier unsafe-options gate work, but no public issue describing this current joined-short-option residual bypass in 3.1.50.
• GitHub issue search for multi_options unsafe found PR #2130, which fixed splitting of multi_options before checking. The current issue remains after that split because -u<value> is treated as option name u<value>, not blocked short option u.
• GitHub issue searches for u<upload-pack> unsafe and -cfoo returned no results.

Suggested remediation:

When checking unsafe Git options, parse joined short options that take values. For clone, -uVALUE and -cKEY=VALUE should be canonicalized to u and c respectively before comparing against the unsafe option set.

A safer approach is to maintain command-specific metadata for unsafe short options and recognize the bare option, split form, joined form, and long --option=<value> / --option <value> forms.