PT-2026-47549 · Pypi · Dulwich

Published

2026-06-08

·

Updated

2026-06-08

CVSS v3.1

3.3

Low

VectorAV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

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 /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

Path traversal

Weakness Enumeration

CWE-22

Related Identifiers

GHSA-555P-6GRF-MH7F

Affected Products

Dulwich