Werkzeug safe_join() allows Windows special device names
Werkzeug's safe_join function allows path segments with Windows device names. On Windows, there are special device names such as CON, AUX, etc that are implicitly present and readable in every directory. 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.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | werkzeug | < 3.1.4 | 3.1.4 |
References
- https://github.com/pallets/werkzeug/security/advisories/GHSA-hgf8-39gv-g3f2
- https://nvd.nist.gov/vuln/detail/CVE-2025-66221
- https://github.com/pallets/werkzeug/commit/4b833376a45c323a189cd11d2362bcffdb1c0c13
- https://github.com/pallets/werkzeug
- https://github.com/pallets/werkzeug/releases/tag/3.1.4
- https://pypi.org/project/werkzeug
- https://github.com/advisories/GHSA-hgf8-39gv-g3f2
- 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
- 02.12.2025
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-2046 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-hgf8-39gv-g3f2 - 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
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Werkzeug safe_join() allows Windows special device names this entry
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