GitPython: Arbitrary file truncation via git rev-list --output argument injection in unguarded Commit.count

Summary

Commit.count() forwards **kwargs into rev_list with no check_unsafe_options guard (the guard exists only in the sibling iter_items, commit.py:341). git rev-list --output=<path> opens and truncates the target file to 0 bytes before revision parsing, so count(output='/victim') destroys/blanks an arbitrary file.

Root Cause

commit.py:290-291 calls self.repo.git.rev_list(self.hexsha, **kwargs) with no check_unsafe_options and no allow_unsafe_options parameter. The sibling iter_items (commit.py:341) is guarded; count is not. This is a distinct, uncovered sink — GHSA-956x-8gvw-wg5v fixed iter_commits/blame, not count.

Impact

Destroy/blank an arbitrary file at process privilege (integrity/availability). Reachability is key-control only (count uses self.hexsha, not a user ref), and the write is a 0-byte truncation (no content control), so MEDIUM.

Proof of Concept

commit.count(output='/path/to/victim')   # victim truncated to 0 bytes (verified)
# control: commit.iter_commits(output=...) raises UnsafeOptionError

Attack Chain

1. Entry: app forwards user options -> commit.count(output='/victim'). Guard: none. Bypass proof: iter_commits(output=) raises UnsafeOptionError; count(output=) does not — verified side-by-side.
2. Sink: git rev-list <sha> --output=/victim -> file truncated to 0 bytes. Impact: destroy/blank arbitrary file.

Bypass Evidence

Live-verified on HEAD (tag 3.1.53): count(output=<victim>) truncated a pre-existing file to 0 bytes; guarded iter_commits(output=) raised UnsafeOptionError. Same CNA-accepted "app forwards user options dict" model as GHSA-956x-8gvw-wg5v's archive(**kwargs). Uncovered sink, not a duplicate.

Affected Versions

<= 3.1.53

Suggested Fix

Add check_unsafe_options to Commit.count (mirroring iter_items).

Reported by zx (Jace) — GitHub: @manus-use