# CVE-2026-122299: Dulwich before 1.2.20 Commit Parser Tree Header Misinterpretation

Status: published. Published: 2026-11-04. Updated: 2026-11-04.

Dulwich before 1.2.20 contains a commit object parsing vulnerability where the read path in _parse_commit resolves a duplicate tree header to the last occurrence instead of the first, diverging from core git's resolution behavior, while Poetry 2.5.1 ships this version and uses dulwich by default for git dependency installation. Attackers can craft a commit object with two tree headers so that reviewers and CI using git see a benign tree while Poetry's dulwich-based checkout resolves to a different attacker-controlled tree containing malicious build scripts such as setup.py, resulting in unreviewed code execution on the install or build host.

## Remediation

- fix: The reporting source identifies this reference as a patch. Check the advisory for affected versions and supported release branches. (source: CNA: VulnCheck) — https://github.com/jelmer/dulwich/releases/tag/dulwich-1.2.20

## Affected products and versions

- jelmer / dulwich (jelmer/dulwich): ≥ 0; < 1.2.20 (affected, semver). Source: CNA: VulnCheck

## Severity and prioritization

- CVSS 4.0: 8.6 (high); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N; source: CNA: VulnCheck

- CVSS 3.1: 8.8 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H; source: CNA: VulnCheck

- CVSS 4.0: 8.6 (high); CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X; source: NVD: disclosure@vulncheck.com

- CVSS 3.1: 8.8 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H; source: NVD: disclosure@vulncheck.com

- CISA KEV: No listing in collected sources

- EPSS: Not available

- SSVC: Not available

- Weaknesses: CWE-1250, CWE-115

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://github.com/jelmer/dulwich/releases/tag/dulwich-1.2.20 (CNA: VulnCheck; patch, release-notes)

- https://github.com/jelmer/dulwich/commit/b77f385b4b0d2d2c7f5ac39dae628948f7ad3a96 (CNA: VulnCheck; issue-tracking)

- https://www.vulncheck.com/advisories/dulwich-before-commit-parser-tree-header-misinterpretation (CNA: VulnCheck; third-party-advisory)

- https://github.com/jelmer/dulwich/commit/b77f385b4b0d2d2c7f5ac39dae628948f7ad3a96 (disclosure@vulncheck.com)

- https://github.com/jelmer/dulwich/releases/tag/dulwich-1.2.20 (disclosure@vulncheck.com)

- https://www.vulncheck.com/advisories/dulwich-before-commit-parser-tree-header-misinterpretation (disclosure@vulncheck.com)

## Provenance

- CNA: VulnCheck: https://www.cve.org/CVERecord?id=CVE-2026-122299; retrieved 2026-11-04; source updated 2026-11-04

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-122299; retrieved 2026-11-05; source updated 2026-11-04

Revision: 80510c7db75fedb99d34c0d223876b2c3158db1c1d5fe1cacfc7d78c2f787697

Canonical: https://y2.dev/cve/CVE-2026-122299

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