CVE-2026-27199
MEDIUMWerkzeug < 3.1.6 - Denial of Service via Windows Device Name Path Handling
Title source: llmExploitation Summary
EIP tracks 2 public exploits for CVE-2026-27199. PoCs published by XiaomingX, alimezar.
AI-analyzed exploit summary This repository contains a functional proof-of-concept exploit for CVE-2026-27199, demonstrating a bypass in Werkzeug's `safe_join()` function on Windows that allows access to device files (e.g., NUL) via nested path segments. The PoC includes a Python script that tests the vulnerability and confirms silent data loss when writing to a bypassed device path.
Description
Werkzeug is a comprehensive WSGI web application library. Versions 3.1.5 and below, the safe_join function allows Windows device names as filenames if preceded by other path segments. This was previously reported as GHSA-hgf8-39gv-g3f2, but the added filtering failed to account for the fact that safe_join accepts paths with multiple segments, such as example/NUL. The function send_from_directory uses safe_join to safely serve files at user-specified paths under a directory. If the application is running on Windows, and the requested path ends with a special device name, the file will be opened successfully, but reading will hang indefinitely. This issue has been fixed in version 3.1.6.
Exploits (2)
This repository contains a functional proof-of-concept exploit for CVE-2026-27199, demonstrating a bypass in Werkzeug's `safe_join()` function on Windows that allows access to device files (e.g., NUL) via nested path segments. The PoC includes a Python script that tests the vulnerability and confirms silent data loss when writing to a bypassed device path.
This repository contains a functional proof-of-concept exploit for CVE-2026-27199, demonstrating a bypass in Werkzeug's `safe_join()` function on Windows systems. The exploit shows how nested device names (e.g., 'subdir/NUL') bypass the security check, leading to silent data loss or indefinite read hangs.
References (3)
Scores
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L