Vulnerability in Microsoft Windows
CVE-2026-21860
Werkzeug is a comprehensive WSGI web application library. Prior to version 3.1.5, Werkzeug's safe_join function allows path segments with Windows device names that have file extensions or trailing spaces. On Windows, there are special device names such as CON, AUX, etc that are implicitly present and readable in every directory. Windows still accepts them with any file extension, such as CON.txt, or trailing spaces such as CON. This issue has been patched in version 3.1.5.
EPSS: 0.005 (37.7th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.
Affected products
- Microsoft Windows
- Pallets Werkzeug — versions < 3.1.5
- Palletsprojects Werkzeug
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Vendor Advisory)
- security-advisories@github.com (Patch, x_refsource_MISC)
Frequently asked questions
- What is CVE-2026-21860?
- CVE-2026-21860 is a medium-severity vulnerability in Microsoft Windows, classified under CWE-67. CVSS score: 5.3/10. Published 2026-01-08.
- How severe is CVE-2026-21860?
- Medium severity. CVSS v3 base score is 5.3 out of 10.