{"id":"PYSEC-2026-2462","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 \u003coutdir\u003e/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","aliases":["CVE-2026-47712","GHSA-555p-6grf-mh7f"],"modified":"2026-07-13T16:31:45.177098535Z","published":"2026-07-13T15:46:15.563670Z","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"}],"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"],"database_specific":{"source":"https://github.com/pypa/advisory-database/blob/main/vulns/dulwich/PYSEC-2026-2462.yaml"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N"}]}