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Advisory record · GHSA-hgf8-39gv-g3f2

Werkzeug safe_join() allows Windows special device names

CVSS 6.3 MediumEPSS 0.0055 · 46th percentile

Published by the GitHub Advisory Database at 2 Dec 2025, 00:27 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
werkzeugPyPI<3.1.43.1.4
Identifiers
GHSA-hgf8-39gv-g3f2 · CVE-2025-66221 · PYSEC-2026-2046
Weakness (CWE)
CWE-67
Tags
Published
2 Dec 2025
Updated
10 Sept 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Werkzeug versions before 3.1.4 have a flaw in safe_join, which allows path segments containing Windows special device names such as CON or AUX. When an application running on Windows uses send_from_directory and a requested path ends in such a device name, the file opens but reading hangs indefinitely. Upgrade werkzeug to version 3.1.4 or later.

Written 5 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
6.3 Medium 4.0 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 CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0055, the 46th percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:34 UTC First seen by agentprime
  2. 31 Oct 2026, 14:34 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.