Werkzeug safe_join() allows Windows special device names

MEDIUM 5.3CVE-2025-66221 · GHSA-hgf8-39gv-g3f2 · PYSEC-2026-2046 · Published 29/11/2025 · updated 07/10/2026

Package	Affected versions	Patched versions
werkzeug PyPI	`< 3.1.4`	`3.1.4`
werkzeug palletsprojects	`< 3.1.4`	`3.1.4`

Description

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.

NVD description

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.

References

pallets/werkzeug security advisory · WEB
nvd.nist.gov/vuln/detail/CVE-2025-66221 · ADVISORY
pallets/werkzeug commit 4b83337 · WEB
pallets/werkzeug · PACKAGE
pallets/werkzeug release 3.1.4 · WEB
pypi.org/project/werkzeug · PACKAGE
GitHub Advisory GHSA-hgf8-39gv-g3f2 · ADVISORY

Running one of these products? Scan your site to see whether it exposes a vulnerable version.

Scan my site free

Package

Affected versions

Patched versions

werkzeug

PyPI

< 3.1.4

3.1.4

werkzeug

palletsprojects

< 3.1.4

3.1.4

Description

NVD description