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Advisory record · GHSA-29vq-49wr-vm6x

Werkzeug safe_join() allows Windows special device names

CVSS 6.3 MediumEPSS 0.0063 · 50th percentile

Published by the GitHub Advisory Database at 19 Feb 2026, 20:32 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
werkzeugPyPI<3.1.63.1.6
Identifiers
GHSA-29vq-49wr-vm6x · CVE-2026-27199 · PYSEC-2026-2320
Weakness (CWE)
CWE-67
Tags
Published
19 Feb 2026
Updated
10 Sept 2026

Machine-written summary

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

Werkzeug versions before 3.1.6 have a flaw in safe_join, which lets Windows device names such as NUL pass through when they follow other path segments. An application on Windows that uses send_from_directory with a user-controlled path can be made to open such a device name, and reading from it hangs indefinitely, which can cause a denial of service. Upgrade werkzeug to version 3.1.6 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 0.0063, the 50th 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.