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.
How to fix
- palletsprojects werkzeug3.1.6 or later
- werkzeug3.1.6 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| palletsprojects werkzeug | v < 3.1.6 | 3.1.6 |
| werkzeugPyPI | v < 3.1.6 | 3.1.6 |
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Attack Surface Management
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