CVE-2026-102598: 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.
References
- github.com/advisories/GHSA-g6x2-hccm-hh4m
- github.com/pallets/werkzeug/commit/8d77320bcdf3a34941ec06dcf16b03c065cd21b6
- github.com/pallets/werkzeug/pull/3309
- github.com/pallets/werkzeug/releases/tag/3.1.9
- github.com/pallets/werkzeug/security/advisories/GHSA-g6x2-hccm-hh4m
- nvd.nist.gov/vuln/detail/CVE-2026-102598
Code Behaviors & Features
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