# Dulwich arbitrary file write on Windows via unvalidated drive letters

Source: https://junglewise.ai/threats/dulwich-arbitrary-file-write-rce-on-windows-via-unvalidated-drive-fc90311d  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-02. Updated: 2026-10-02  
License: CC BY 4.0 with a link back

Severity: high · CVSS 8.8 · Published 2026-10-02

Dulwich is a Python library that implements Git functionality. On Windows, it fails to validate DOS drive letter prefixes in Git tree paths, allowing an attacker to write files outside the intended repository directory. A malicious repository could write files to arbitrary locations like the user's home directory or startup folders, leading to remote code execution or system compromise.

Technologies: [Dulwich](https://junglewise.ai/threats/technologies/dulwich-dulwich), [dulwich (PyPI)](https://junglewise.ai/threats/technologies/dulwich). Vendors: [Dulwich](https://junglewise.ai/threats/vendors/dulwich), [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is This vulnerability exploited in the wild?** No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

**How severe is This vulnerability?** High severity, with a CVSS score of 8.8, published 2 October 2026.

**Which products and versions are affected?** Dulwich all versions prior to fix; dulwich (PyPI) < 1.2.9.

**Is there a fix for This vulnerability?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is This vulnerability attacked?** It is attacked over the network, in a software library.

**Am I affected?** Check whether you run Dulwich or dulwich (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A path traversal vulnerability exists in Dulwich's NTFS path validation functions (validate_path_element_ntfs and _tree_to_fs_path) which reject reserved names and alternate data streams but miss DOS drive letter checks. When os.path.join() on Windows receives an absolute drive letter path as the second argument, it discards the root path; an attacker can craft a malicious Git tree with entries named "C:" to write files to arbitrary absolute paths. The vulnerability is triggered during repository checkout without requiring authentication.

## Affected products

- Dulwich Dulwich all versions prior to fix

## Timeline

- 2026-10-02: disclosed

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