GHSA-hh9p-6wh2-4mfc

## Summary

`IndexFile.remove()` and `Head.checkout()` forward `**kwargs` into `git rm` and `git checkout` with no guard. Passing `--pathspec-from-file=<file>` **together with `--pathspec-file-nul`** makes Git treat the whole file as a single NUL-delimited pathspec, and the unmatched-pathspec error quotes it verbatim. GitPython surfaces that through `GitCommandError.stderr`, so the entire contents of a caller-chosen file are returned to the caller in band.

This is the same primitive as Instance 2 of [GHSA-3f7w-8rr8-f37f](https://github.com/advisories/GHSA-3f7w-8rr8-f37f) - `TagReference.create()` with `-F`, arbitrary file read returned in band - at two sites that advisory assessed and cleared.

## Prior art, and why I am filing rather than commenting

GHSA-3f7w-8rr8-f37f's sweep table lists these four sites with the assessment *"`--pathspec-from-file` only reads a pathspec; no write or disclosure primitive found"*:

| Call site | git command | that advisory's assessment | |---|---|---| | `IndexFile.remove()` | `rm` | `--pathspec-from-file` only reads a pathspec; no write or disclosure primitive found | | `IndexFile.move()` | `mv` | same | | `HEAD.reset()` | `reset` | same | | `HEAD.checkout()` | `checkout` | same |

That assessment is very nearly right, and I think that is why it held: with `--pathspec-from-file` alone, Git splits on newlines and the error quotes only the **first line**, which reads as an uninteresting partial. Adding `--pathspec-file-nul` - a sibling flag of the same option, and the documented way to handle paths containing newlines - makes the whole file one pathspec.

## Root cause

`git/index/base.py:991-1043`:

```python def remove(self, items, working_tree=False, **kwargs): ... removed_paths = self.repo.git.rm(args, paths, **kwargs).splitlines() # line 1043 ```

`git/refs/head.py:237-268`:

```python def checkout(self, force: bool = False, **kwargs: Any): ... self.repo.git.checkout(self, **kwargs) # line 268 ```

Neither has an `allow_unsafe_options` parameter or a `check_unsafe_options()` call.

## Proof of concept

```python from git import Repo from git.exc import GitCommandError

repo = Repo("/path/to/repo") kw = dict(pathspec_from_file="/etc/passwd", pathspec_file_nul=True)

try: repo.index.remove([], **kw) # or: repo.heads[0].checkout(**kw) except GitCommandError as e: print(e.stderr) # <- entire file contents ```

Observed on published 3.1.57, against a canary file holding three marked lines:

``` [PASS] IndexFile.remove() -> `git rm` returns ALL 3 canary lines in-band stderr: 'fatal: pathspec 'LINE1-CANARY-4242 LINE2-SECRET-7777 LINE3-TAIL-9999 ' did not match any files' [PASS] Head.checkout() -> `git checkout` returns ALL 3 canary lines in-band stderr: 'error: pathspec 'LINE1-CANARY-4242 LINE2-SECRET-7777 LINE3-TAIL-9999 ' did not match any file(s) known to git' [PASS] PRECISION: `git status` leaks 0/3 -- not every unguarded site discloses [PASS] PRECISION: the GUARDED checkout-index leaks 0/3 ```

The two precision controls are there so the result is about these sinks and not about the canary being visible everywhere.

## Scope correction to the table above

Of the four sites cleared with that sentence, **two disclose and two do not**:

| Call site | disclosed? | |---|---| | `IndexFile.remove()` → `git rm` | **yes, full file** | | `Head.checkout()` → `git checkout` | **yes, full file** | | `HEAD.reset()` → `git reset` | no - `git reset` does not error on unmatched pathspecs | | `IndexFile.move()` → `git mv` | no |

The two negatives are mentioned because "the dismissal was wrong" would overstate it: the dismissal was wrong for half of what it covered.