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CVE-2026-47712 — Dulwich doesn't sanitize commit subjects in `porcelain.format_patch`

2026-09-29T07:34:49.313816+00:00

Affected: jelmer dulwich

Dulwich is a pure-Python implementation of the Git file formats and protocols. Starting in version 0.24.0 and prior to version 1.2.5, 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. This is fixed in Dulwich 1.2.5. Users should upgrade to 1.2.5 or later. 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. 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; and/or pre-screen commits a…

GHSA-555p-6grf-mh7f — Dulwich doesn't sanitize commit subjects in `porcelain.format_patch`

2026-09-29T07:34:49.314011+00:00

Affected: PyPI: dulwich

### 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 char…

PYSEC-2026-2462 — Dulwich doesn't sanitize commit subjects in `porcelain.format_patch`

2026-09-29T07:34:49.314114+00:00