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Moderate severityNVD Advisory· Published Feb 21, 2026· Updated Feb 24, 2026

Werkzeug safe_join() allows Windows special device names

CVE-2026-27199

Description

Werkzeug is a comprehensive WSGI web application library. Versions 3.1.5 and below, the safe_join function allows Windows device names as filenames if preceded by other path segments. This was previously reported as GHSA-hgf8-39gv-g3f2, but the added filtering failed to account for the fact that safe_join accepts paths with multiple segments, such as example/NUL. The function 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 fixed in version 3.1.6.

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Affected packages

Versions sourced from the GitHub Security Advisory.

PackageAffected versionsPatched versions
werkzeugPyPI
< 3.1.63.1.6

Affected products

36

Patches

Vulnerability mechanics

References

5

News mentions

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