Vulnerability · Published Feb 21, 2026 · Assigned by GitHub_M
CVE-2026-27199Werkzeug safe_join() allows Windows special device names
Medium 6.3
In plain English
A medium-severity security flaw in werkzeug from pallets. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 50% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code. Fixed versions are available - upgrade the affected package.
Official description
Werkzeug is a comprehensive WSGI web application library. Versions 3.1.5 and below, the safe_join function allows Windows device names as filenames if preceded by other path segments. This was previously reported as GHSA-hgf8-39gv-g3f2, but the added filtering failed to account for the fact that safe_join accepts paths with multiple segments, such as example/NUL. The function 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. This issue has been fixed in version 3.1.6.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.24 | py3-werkzeug | 3.1.6-r0 | ALPINE-CVE-2026-27199 |
| PyPI | werkzeug | 3.1.6 | GHSA-29vq-49wr-vm6x |
| PyPI | werkzeug | 3.1.6 | PYSEC-2026-2320 |
Affected products (as reported)
Weakness: CWE-67 · 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
References
- https://github.com/pallets/werkzeug/security/advisories/GHSA-29vq-49wr-vm6x x_refsource_CONFIRM
- https://github.com/pallets/werkzeug/commit/f407712fdc60a09c2b3f4fe7db557703e5d9338d x_refsource_MISC
- https://github.com/pallets/werkzeug/releases/tag/3.1.6 x_refsource_MISC