GHSA-hgf8-39gv-g3f2

Werkzeug safe_join() allows Windows special device names

Source: GitHub Advisory Database (reviewed) Moderate CVE-2025-66221

Packages

Ecosystem	Package	Affected	Fixed in
PyPI	werkzeug	< 3.1.4	3.1.4

Details

As written in the advisory (Markdown source, shown as plain text).

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.

References

External links from the advisory. They lead to third-party sites.

https://github.com/pallets/werkzeug/security/advisories/GHSA-hgf8-39gv-g3f2 web
https://nvd.nist.gov/vuln/detail/CVE-2025-66221 advisory
https://github.com/pallets/werkzeug/commit/4b833376a45c323a189cd11d2362bcffdb1c0c13 web
https://github.com/pallets/werkzeug package
https://github.com/pallets/werkzeug/releases/tag/3.1.4 web