---
id: CVE-2026-47712
aliases:
  - GHSA-555p-6grf-mh7f
title: Dulwich doesn't sanitize commit subjects in `porcelain.format_patch`
summary: Dulwich doesn't sanitize commit subjects in `porcelain.format_patch`
severity: low
cvss: 3.3
cwe:
  - CWE-22
vendor: dulwich
product: dulwich
ecosystem: pip
affected:
  - 'dulwich >= 0.24.0, < 1.2.5'
patched:
  - dulwich 1.2.5
published: '2026-06-08'
updated: '2026-06-11'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-555p-6grf-mh7f'
references:
  - url: 'https://github.com/jelmer/dulwich/security/advisories/GHSA-555p-6grf-mh7f'
  - url: 'https://github.com/jelmer/dulwich/commit/c2446e51b'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-47712'
  - url: 'https://github.com/jelmer/dulwich/releases/tag/dulwich-1.2.5'
  - url: 'https://github.com/advisories/GHSA-555p-6grf-mh7f'
tags:
  - ghsa
  - pip
epss: 0.00177
epssPercentile: 0.06443
ingestedAt: '2026-07-07T15:41:59.842Z'
---

## Overview

### Impact

dulwich.porcelain.format_patch(outdir=...) derives each patch filename from the commit's subject line. Prior to this fix, get_summary only replaced spaces with dashes - path separators (/, \),   parent-directory components (..), and   other filename-hostile characters (e.g. :)  were preserved verbatim and passed   straight into os.path.join(outdir,   f"{i:04d}-{summary}.patch").

A malicious commit subject could therefore direct the generated patch file outside the requested outdir. Reduced examples:

- x/../../x produced <outdir>/0001-x/../../x.patch, resolving
  two directories above outdir.
- x\..\..\x produced the equivalent escape on Windows, here \ is also a path separator.

Related issues from the same root cause:

- Subjects containing characters that are illegal in Windows filenames (e.g. :) caused format_patch to fail outright on  Windows, where git would have succeeded.
- Very long subjects produced excessively long filenames that could exceed filesystem limits; git truncates them.

Anyone calling porcelain.format_patch (or the dulwich format-patch CLI) against untrusted commits - for example, a service that runs format-patch over user-supplied repositories or pull requests - could have patch files written to attacker-chosen locations within the process's write permissions.

### Patches

Fixed in Dulwich 1.2.5. Users should upgrade.

 dulwich.patch.get_summary now mirrors git's format_sanitized_subject: only `[A-Za-z0-9._]` are kept, runs of other characters collapse to a single -, consecutive . collapse to a single ., trailing ./- are stripped, and the result is length-limited. This makes the returned string safe to embed as a filename component, so format_patch can no longer be steered out of outdir via the commit subject.

###  Workarounds

Until upgrading, callers that pass untrusted commits to   porcelain.format_patch can:

- Use stdout=True and write the patch to a destination they control, rather than letting format_patch choose the filename.
- Validate the chosen path before opening - e.g. compare os.path.realpath(returned_path) against  os.path.realpath(outdir) and reject any patch whose resolved path is not inside outdir.
- Pre-screen commits and refuse to format any whose subject's first line contains /, \, .., or other characters that are not safe on the target filesystem.

### Resources

- Fix commit: https://github.com/jelmer/dulwich/commit/c2446e51b
- Affected API: dulwich.porcelain.format_patch / dulwich format-patch
- Reference behavior: git's format_sanitized_subject in pretty.c

## Affected packages

- `dulwich >= 0.24.0, < 1.2.5`

## Remediation

Upgrade to a patched release:

- `dulwich 1.2.5`