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GHSA-cm62-gvxx-vmxx

HighCVSS 8.6 / 10
Published Oct 2, 2026·Last modified Oct 2, 2026
Affected Components(1)
PyPI logodulwich
0.22.5 – 1.2.8
Description

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)

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Risk Scores
Base Score
8.6

The vulnerability requires local access to the device to be exploited. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. The attacker needs the user to perform some action, like clicking a link. The vulnerability can affect other systems as well, not just the initial system. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.

Threat Intelligence
7.9

Exploitation activity has been observed. Apply available patches or mitigations urgently.

EPSS
N/A

Probability that this vulnerability will be exploited in the wild within the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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High severity
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