Affected: gitpython-developers GitPython

GitPython before 3.1.54 contains an incomplete denylist in unsafe_git_clone_options that omits --template, allowing attackers to achieve arbitrary command execution during clone operations. Attackers can supply --template pointing to a directory containing malicious post-checkout hooks that execute when git clones the repository.

Affected: PyPI: GitPython

## Summary GitPython's `unsafe_git_clone_options` denylist omits `--template`. `git clone --template=<dir>` copies `<dir>/hooks/` into the new repository and runs them (`post-checkout` fires during clone), so a caller who can influence clone options can achieve arbitrary command execution in the default `allow_unsafe_options=False` configuration.

## Root Cause `base.py:145-152` defines `unsafe_git_clone_options = ["--upload-pack","-u","--config","-c"]` — `--template` is absent. The guard candidate `['--template']` passes `check_unsafe_options` (verified). git copies the hook directory and executes `post-checkout` at checkout time. git's `protocol.allow`/`GIT_ALLOW_PROTOCOL` do not gate `--template`; the incomplete denylist is the only defense.

## Impact Arbitrary OS command execution during clone (default config). Requires an attacker-readable directory containing an executable hook — a genuine second precondition (realistic via shared filesystems, upload dirs, `/tmp`, or attacker-writable network paths), reflected as AC:H.

## Proof of Concept ```python # attacker stages <dir>/hooks/post-checkout (chmod +x) from git import Repo Repo.clone_from(src, dst, template='<dir>') # post-checkout hook executes -> marker created (verified) ```

## Attack Chain 1. Setup: attacker stages `<dir>/hooks/post-checkout` (chmod +x). Guard: n/a (filesystem). 2. Entry: `Repo.clone_from(url, path, template='<dir>')`. Guard: `check_unsafe_options(candidates=['--template'], unsafe=unsafe_git_c…

Affected: PyPI: gitpython

GitPython before 3.1.54 contains an incomplete denylist in unsafe_git_clone_options that omits --template, allowing attackers to achieve arbitrary command execution during clone operations. Attackers can supply --template pointing to a directory containing malicious post-checkout hooks that execute when git clones the repository.