Werkzeug safe_join() allows Windows special device names
Werkzeug's `safe_join` function allows Windows device names as filenames when they have an empty ADS marker on NTFS. This was previously reported as https://github.com/pallets/werkzeug/security/advisories/GHSA-hgf8-39gv-g3f2, but the added filtering failed to account for the fact Windows allows special device names with an empty ADS marker, such as `NUL:`. `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 NTFS, and the requested path ends with a special device name, the file will be opened successfully, but reading will hang indefinitely.
describes (1)
Related CVEs.
| ID | severity | exploitable | ||
|---|---|---|---|---|
| CVE-2026-102598US | — | — | ||
Werkzeug is a comprehensive WSGI web application library. Prior to 3.1.9, the safe_join function used by send_from_directory can allow a NUL: special-device path because safe_join… | ||||
references
External citations — patches, advisories, analysis.
- https://github.com/advisories/GHSA-g6x2-hccm-hh4mADVISORY
- https://github.com/pallets/werkzeugPACKAGE
- https://github.com/pallets/werkzeug/commit/8d77320bcdf3a34941ec06dcf16b03c065cd21b6WEB
- https://github.com/pallets/werkzeug/pull/3309WEB
- https://github.com/pallets/werkzeug/releases/tag/3.1.9WEB
- https://github.com/pallets/werkzeug/security/advisories/GHSA-g6x2-hccm-hh4mWEB
- https://nvd.nist.gov/vuln/detail/CVE-2026-102598ADVISORY
- https://pypi.org/project/werkzeugPACKAGE
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