GitHub Advisoryadvisory · PyPI

GHSA-87hc-h4r5-73f7 Werkzeug safe_join() allows Windows special device names with compound extensions

MEDIUM Published 2026-01-08 Modified 2026-02-02 Official page ↗
Aliases
CVE-2026-21860
Ecosystem
PyPI
Packages
Werkzeug
Severity
Moderate
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Weaknesses
CWE-67
Reviewed
2026-01-08

Affected packages

• PyPI Werkzeug: < 3.1.5 → fixed in 3.1.5

Description

Werkzeug's `safe_join` function allows path segments with Windows device names that have file extensions or trailing spaces. On Windows, there are special device names such as `CON`, `AUX`, etc that are implicitly present and readable in every directory. Windows still accepts them with any file extension, such as `CON.txt`, or trailing spaces such as `CON `. This was previously reported as https://github.com/pallets/werkzeug/security/advisories/GHSA-hgf8-39gv-g3f2, but the fix failed to account for compound extensions such as `CON.txt.html` or trailing spaces. It also missed some additional special names. `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-2026-21860 Werkzeug is a comprehensive WSGI web application library. vulnerability

Weakness · CWE (1)

  • CWE-67 Improper Handling of Windows Device Names weakness

References