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High

Dulwich: Symlink directory traversal in stash pop allows arbitrary file write via intermediate directory symlinks

  • Disclosed: 02.10.2026
  • Updated: 11.10.2026 15:18

Summary

Dulwich's stash.py:pop() function is vulnerable to symlink directory traversal, allowing an attacker to write arbitrary files outside the repository worktree when a victim pops a stash in a malicious repository.

Root Cause

The pop() function at dulwich/stash.py:236 uses os.path.exists(parent_dir) to check if a parent directory exists before writing stashed files. os.path.exists() follows symlinks, so when an intermediate directory in the path is a symlink pointing outside the worktree (e.g., link → ../../.git/hooks), the check passes and subsequent file writes resolve through the symlink.

The validate_path() function (line 228) only validates path component names against INVALID_DOTNAMES — it performs zero filesystem symlink detection. On dulwich 1.2.7 (latest release), build_file_from_blob() has no symlink protection whatsoever.

Impact

An attacker can craft a malicious repository that, when a victim clones it and performs a stash pop operation, writes attacker-controlled content to arbitrary filesystem locations. Writing to .git/hooks/post-checkout achieves Remote Code Execution on the victim's machine on the next git checkout operation.

Attack Scenario

  1. Attacker creates a repository with branch main containing link (symlink → ../../.git/hooks) and branch feature containing link/post-checkout (executable payload)
  2. Victim clones the repository (landing on main — symlink link exists in worktree)
  3. Victim checks out feature, makes changes, runs stash.push()
  4. Victim checks out main (restoring the link symlink)
  5. Victim runs stash.pop(0) — stash contains link/post-checkout
  6. os.path.exists("link") returns True (symlink to existing directory), os.makedirs skipped
  7. build_file_from_blob(blob, mode, "link/post-checkout") → open("link/post-checkout", "wb") follows the intermediate symlink → payload written to .git/hooks/post-checkout
  8. Next checkout operation triggers the hook → RCE

Suggested Fix

Before writing any file, verify that no component of the target path resolves through a symlink outside the worktree. Use os.path.realpath(parent_dir) and confirm it stays within the repository root. Alternatively, use os.open() with O_NOFOLLOW on each path component.

Reported by zx (Jace)

Affected software

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PlatformPackageVulnerable versionsFixed in
Python (PyPI) dulwich >= 0.22.5, < 1.2.8 1.2.8

References

CVSS score 8.6/10
CVSS vector
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
Weakness (CWE)
CWE-22, CWE-59
Platform
Python (PyPI)
Package
dulwich
Disclosed
02.10.2026
Updated
11.10.2026 15:18

Sources and licenses

OSV / GitHub Advisory Database - GHSA-cm62-gvxx-vmxx - CC BY 4.0

Vulnerability history: dulwich

All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (13) in the archive
Total entries
13
First → latest
03.2015 10.2026
Without a fix
0
Exploited in attacks
0

Severity breakdown

  • Critical 3
  • High 7
  • Medium 2
  • Low 1

Disclosures per year

earlier: 2

Severity:
  1. Dulwich: Arbitrary File Write (RCE) on Windows via Unvalidated Drive Letters in Tree Paths
    High · 8.8 ghsa-8mcx-5rqc-vhmf < 1.2.9 1.2.9
  2. Dulwich: Symlink write-through in checkout(paths=[]) via raw os.open bypasses all symlink protections
    High · 8.6 ghsa-8w8g-wq8h-fq33 >= 0.24.0, < 1.2.8 1.2.8
  3. Dulwich: Symlink directory traversal in filter-branch index_filter via cross-commit state persistence
    High · 8.6 ghsa-5fqc-mrg8-w798 >= 0.23.1, < 1.2.8 1.2.8
  4. Dulwich: Symlink directory traversal in stash pop allows arbitrary file write via intermediate directory symlinks this entry
    High · 8.6 ghsa-cm62-gvxx-vmxx >= 0.22.5, < 1.2.8 1.2.8
  5. Dulwich's submodule path traversal in porcelain.submodule_update / porcelain.clone(recurse_submodules=True) yields RCE via attacker-dropped .git/hooks payload
    High · 7.5 CVE-2026-52726 >= 0.23.2, < 1.2.5 1.2.5
  6. Dulwich Vulnerable to Command Injection via Merge Driver Path
    High CVE-2026-42563 >= 0.24.0, < 1.2.5 1.2.5
  7. Dulwich has an arbitrary file write via NTFS-hostile tree entries on Windows
    High · 8.8 CVE-2026-42305 >= 0.10.0, < 1.2.5 1.2.5
  8. Dulwich before 0.18.5, when an SSH subprocess is used, allows remote attackers to execute arbitrary commands via an ssh URL with an initial dash character in the hostname, a related issue to CVE-2017-
    Critical · 9.8 CVE-2017-16228 < 0.18.5 0.18.5
  9. The build_index_from_tree function in index.py in Dulwich before 0.9.9 allows remote attackers to execute arbitrary code via a commit with a directory path starting with .git/, which is not properly h
    Critical · 9.8 CVE-2014-9706 < 0.9.9 0.9.9
  10. Buffer overflow in the C implementation of the apply_delta function in _pack.c in Dulwich before 0.9.9 allows remote attackers to execute arbitrary code via a crafted pack file.
    Critical · 9.8 CVE-2015-0838 < 0.9.9 0.9.9

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