GitHub Advisoryadvisory · PyPI

GHSA-29vq-49wr-vm6x Werkzeug safe_join() allows Windows special device names

MEDIUM Published 2026-02-19 Modified 2026-02-23 Official page ↗
Aliases
CVE-2026-27199
Ecosystem
PyPI
Packages
werkzeug
Severity
Moderate
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
Weaknesses
CWE-67
Reviewed
2026-02-19

Affected packages

• PyPI werkzeug: < 3.1.6 → fixed in 3.1.6

Description

Werkzeug's `safe_join` function allows Windows device names as filenames if when preceded by other path segments. This was previously reported as https://github.com/pallets/werkzeug/security/advisories/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`. `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.

Related

Alias · CVE (1)

  • CVE-2026-27199 Werkzeug is a comprehensive WSGI web application library. vulnerability

Weakness · CWE (1)

  • CWE-67 Improper Handling of Windows Device Names weakness

References