GitHub Advisoryadvisory · PyPI

GHSA-g6x2-hccm-hh4m Werkzeug safe_join() allows Windows special device names

MEDIUM Published 2026-10-05 Modified 2026-10-05 Official page ↗
Aliases
CVE-2026-102598
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
2026-10-05

Affected packages

• PyPI Werkzeug: < 3.1.9 → fixed in 3.1.9

Description

Werkzeug's `safe_join` function allows Windows device names as filenames when they have an empty ADS marker on NTFS. 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 Windows allows special device names with an empty ADS marker, such as `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 NTFS, 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-2026-102598 Werkzeug is a comprehensive WSGI web application library. vulnerability

Weakness · CWE (1)

  • CWE-67 Improper Handling of Windows Device Names weakness

References