PT-2026-111193

Publicado

2026-10-02

·

Atualizado

2026-10-02

Descrição por

CVSS 3.1
8.6
Alta
MétricasAV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

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)
Explorabilidade
Correção
Impactos
Fornecedores
Produtos afetados
Enumeração de fraquezas
CWE-59: Improper Link Resolution Before File Access (\'Link Following\')
CWE-22: Improper Limitation of a Pathname to a Restricted Directory (\'Path Traversal\')
Identificadores relacionados
GHSA-CM62-GVXX-VMXX
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