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.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | werkzeug | < 3.1.9 | 3.1.9 |
References
- https://github.com/pallets/werkzeug/security/advisories/GHSA-g6x2-hccm-hh4m
- https://nvd.nist.gov/vuln/detail/CVE-2026-102598
- https://github.com/pallets/werkzeug/pull/3309
- https://github.com/pallets/werkzeug/commit/8d77320bcdf3a34941ec06dcf16b03c065cd21b6
- https://github.com/pallets/werkzeug
- https://github.com/pallets/werkzeug/releases/tag/3.1.9
- https://pypi.org/project/werkzeug
- https://github.com/advisories/GHSA-g6x2-hccm-hh4m
- CVSS vector
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N- Weakness (CWE)
CWE-67- Platform
- Python (PyPI)
- Package
werkzeug- Disclosed
- 05.10.2026
- Updated
- 15.10.2026 18:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-4312 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-g6x2-hccm-hh4m - CC BY 4.0
Vulnerability history: werkzeug
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 15
- First → latest
- 10.2017 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 4
- Medium 9
- Low 1
- Unrated 1
Disclosures per year
- 2017: 1
- 2018: 0
- 2019: 1
- 2020: 1
- 2021: 0
- 2022: 2
- 2023: 3
- 2024: 3
- 2025: 1
- 2026: 3
-
Werkzeug safe_join() allows Windows special device names this entry
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