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CVE-2026-27199

Werkzeug safe_join() allows Windows special device names

Published: Feb 21, 2026Updated: Mar 3, 2026 Sources: CVE List NVD GHSACWE-67
5.3MEDIUM
NVD MITRE
EPSS Score
0.6%
Top 56.7%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Patch Available
Self-Check
Not available

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.

No summary for this CVE yet.

CVSS Vector Breakdown

AV:NAC:LPR:NUI:NS:UC:NI:NA:L
Exploitability
AV:NAttack Vector
Network
AC:LAttack Complexity
Low
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:NConfidentiality
None
I:NIntegrity
None
A:LAvailability
Low
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Weaknesses

CWE-67

Affected Products

palletsprojects
oss-project·US
werkzeugLibrary
OSS Libraries / pypi
pallets
oss-project·US
werkzeugLibrary
OSS Libraries / pypi
PyPI
package-ecosystem
werkzeug
OSS Libraries

Exploitability

Official Patch Available

References

https://github.com/pallets/werkzeug/commit/f407712fdc60a09c2b3f4fe7db557703e5d9338d
github.com
https://github.com/pallets/werkzeug/releases/tag/3.1.6
github.com
https://github.com/pallets/werkzeug/security/advisories/GHSA-29vq-49wr-vm6x
github.com
and 2 more references View all →

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