CVE-2026-27199
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.
Scoring
- Severity
- MEDIUM
- CVSS base score
- 6.3
- CVSS vector
- CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
- EPSS probability
- 0.56%
- CWE
- CWE-67
- Published
- 2026-02-21
- Last modified
- 2026-03-12
Affected products
- pallets werkzeug
Weakness type
Related vulnerabilities
- CVE-2026-21860 — Werkzeug safe_join() allows Windows special device names with compound extensions
- CVE-2025-66221 — Werkzeug safe_join() allows Windows special device names
- CVE-2024-51745 — Wasmtime doesn't fully sandbox all the Windows device filenames
- CVE-2024-35197 — gix refs and paths with reserved Windows device names access the devices