CVE-2026-27199: 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...

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.

Metrics

CVSS 3.1

5.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS 4.0

6.3/10

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS Probability

0.56%

42.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-67

Affected Software

Vendor	Product	Versions
Palletsprojects	Werkzeug	< 3.1.6

References

Timeline

Published: Feb 21, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-27199?

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 severe is CVE-2026-27199?

CVE-2026-27199 has a CVSS score of 6.3/10 (MEDIUM severity). The EPSS model estimates a 0.56% probability of exploitation in the next 30 days.

How do I fix CVE-2026-27199?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.