CVE-2025-66221 MEDIUM

CVE-2025-66221: Werkzeug safe_join() allows Windows special device names

Vendor Pallets
Product werkzeug
Weakness CWE-67
Published November 29, 2025
Last update December 1, 2025

CVSS base score

6.3/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Confidentiality
Integrity

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

What the vulnerability does

01Description

Werkzeug is a comprehensive WSGI web application library. Prior to version 3.1.4, Werkzeug's safe_join function allows path segments with Windows device names. On Windows, there are special device names such as CON, AUX, etc that are implicitly present and readable in every directory. 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 patched in version 3.1.4.

Key dates

02Disclosure timeline

November 29, 2025 CVE published
December 1, 2025 Record updated