id: PYSEC-2026-2462
published: "2026-07-13T15:46:15.563670Z"
modified: "2026-07-13T16:03:57.395315Z"
aliases:
- CVE-2026-47712
- GHSA-555p-6grf-mh7f
summary: Dulwich doesn't sanitize commit subjects in `porcelain.format_patch`
details: "### Impact\n\ndulwich.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\").\n\nA malicious commit subject could therefore direct the generated patch file outside the requested outdir. Reduced examples:\n\n- x/../../x produced <outdir>/0001-x/../../x.patch, resolving\n  two directories above outdir.\n- x\\..\\..\\x produced the equivalent escape on Windows, here \\ is also a path separator.\n\nRelated issues from the same root cause:\n\n- Subjects containing characters that are illegal in Windows filenames (e.g. :) caused format_patch to fail outright on  Windows, where git would have succeeded.\n- Very long subjects produced excessively long filenames that could exceed filesystem limits; git truncates them.\n\nAnyone 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.\n\n### Patches\n\nFixed in Dulwich 1.2.5. Users should upgrade.\n\n 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.\n\n###  Workarounds\n\nUntil upgrading, callers that pass untrusted commits to   porcelain.format_patch can:\n\n- Use stdout=True and write the patch to a destination they control, rather than letting format_patch choose the filename.\n- 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.\n- 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.\n\n### Resources\n\n- Fix commit: https://github.com/jelmer/dulwich/commit/c2446e51b\n- Affected API: dulwich.porcelain.format_patch / dulwich format-patch\n- Reference behavior: git's format_sanitized_subject in pretty.c"
affected:
- package:
    name: dulwich
    ecosystem: PyPI
    purl: pkg:pypi/dulwich
  ranges:
  - type: ECOSYSTEM
    events:
    - introduced: 0.24.0
    - fixed: 1.2.5
  versions:
  - 0.24.0
  - 0.24.1
  - 0.24.10
  - 0.24.2
  - 0.24.3
  - 0.24.4
  - 0.24.5
  - 0.24.6
  - 0.24.7
  - 0.24.8
  - 0.24.9
  - 0.25.0
  - 0.25.1
  - 0.25.2
  - 1.0.0
  - 1.1.0
  - 1.2.0
  - 1.2.1
  - 1.2.2
  - 1.2.3
  - 1.2.4
references:
- type: WEB
  url: https://github.com/jelmer/dulwich/security/advisories/GHSA-555p-6grf-mh7f
- type: ADVISORY
  url: https://nvd.nist.gov/vuln/detail/CVE-2026-47712
- type: WEB
  url: https://github.com/jelmer/dulwich/commit/c2446e51b
- type: PACKAGE
  url: https://github.com/jelmer/dulwich
- type: WEB
  url: https://github.com/jelmer/dulwich/releases/tag/dulwich-1.2.5
- type: PACKAGE
  url: https://pypi.org/project/dulwich
- type: ADVISORY
  url: https://github.com/advisories/GHSA-555p-6grf-mh7f
severity:
- type: CVSS_V3
  score: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N