CVE-2026-42305 Dulwich has an arbitrary file write via NTFS-hostile tree entries on Windows
Attackers can achieve remote code execution on Windows by tricking users into cloning malicious Git repositories using the Dulwich library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-42305?
CVE-2026-42305 is a high-severity path traversal vulnerability in jelmer dulwich, published on 10 Jun 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Dulwich is a pure-Python implementation of the Git file formats and protocols. Versions starting with 0.10.0 and prior to 1.2.5 have an arbitrary file write leading to remote code execution when cloning or checking out a malicious Git repository on Windows. Dulwich's path-element validator accepted tree entries whose filenames contained bytes that Windows interprets as structural path syntax. Contributing configuration bugs made matters worse. The core.protectNTFS and core.protectHFS settings were looked up under a wrong option name and so user-set values were silently ignored, and core.protectNTFS only defaulted to true on Windows (Git upstream has defaulted it to true everywhere since CVE-2019-1353). Both have been corrected. Anyone who clones, fetches, or checks out an untrusted repository with Dulwich on Windows - either through the Dulwich CLI, porcelain.clone, or any downstream tool built on Dulwich - is impacted. POSIX clones are not directly exploitable (on POSIX \ is a literal filename byte), but a POSIX user can unknowingly propagate a malicious tree to Windows consumers via push or re-publication. This issue is fixed in Dulwich 1.2.5. Users should upgrade to 1.2.5 or later. There is no effective pre-patch workaround. On affected versions the core.protectNTFS configuration key was silently ignored, so setting it to true does not mitigate the issue. Users who cannot upgrade should avoid cloning, fetching, or checking out untrusted repositories with Dulwich on Windows. After upgrading the NTFS validator is on by default on every platform, so no additional configuration is required.
Weakness: CWE-22
Which versions are affected by CVE-2026-42305?
3 open source packages ship an affected version, including dulwich.
| Package | Affected | Fixed in |
|---|---|---|
dulwich PyPI | From 0.10.0 | 1.2.5 |
dulwich PyPI | From 0.10.0 | 1.2.5 |
dulwich PyPI | From 0.10.0 | 1.2.5 |
How do I fix CVE-2026-42305?
Upgrade dulwich to 1.2.5 or later.
Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.
Is CVE-2026-42305 being exploited?
There is no known exploitation of CVE-2026-42305 in the wild and no public exploit code.
Sources
Also known as AZL-90074, CLEANSTART-2026-QB74422, CLSA-2026-1781225617, CLSA-2026-1791190774, ECHO-89fa-d0fd-2f03, GHSA-897w-fcg9-f6xj and 4 more.