🛡️ CVE-2026-27199 — werkzeug

🟡 CVSS 5.3 — Medium ✅ No Known Exploit CWE-67 OSV

5.3

CVSS Score

0 Low4 Medium7 High9 Critical10

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.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. Rated impact: confidentiality none, integrity none, availability low.

Weakness class

CVE-2026-27199 is classified as CWE-67: Improper Handling of Windows Device Names. The product constructs pathnames from user input, but it does not handle or incorrectly handles a pathname containing a Windows device name such as AUX or CON.

Affected software

CVE-2026-27199 is recorded against 1 package.

werkzeug (fixed in 3.1.6)

Timeline and source

Published on 19 February 2026 and last revised on 13 July 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from OSV.

References

github.com (Web)
nvd.nist.gov (Advisory)
github.com (Web)
github.com (Package)
github.com (Web)

CVE-2026-27199 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Alpine PyPI (Root.io)

Details

Severity MEDIUM

CVSS Score 5.3

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

CWE CWE-67

Public Exploit ✅ No

Source OSV

Published 2026-02-19

Updated 2026-08-12

Modified 2026-07-13

Fix URL https://github.com/pallets/werkzeug/commit/f407712fdc60a09c2b3f4fe7db557703e5d9338d

Affected Packages

Software	From version	Fixed in
werkzeug	—	3.1.6

References

WEB https://github.com/pallets/werkzeug/security/advisories/GHSA-29vq-49wr-vm6x

ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2026-27199

WEB https://github.com/pallets/werkzeug/commit/f407712fdc60a09c2b3f4fe7db557703e5d9338d

PACKAGE https://github.com/pallets/werkzeug

WEB https://github.com/pallets/werkzeug/releases/tag/3.1.6

🔗 NVD 🔗 Mitre ✅ Fix / Advisory

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