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Medium severity · published Nov 29, 2025
CVE-2025-66221
Werkzeug is a comprehensive WSGI web application library
5.3
CVSS
0.5%
EPSS
No
On KEV
Description
Werkzeug is a comprehensive WSGI web application library. Prior to version 3.1.4, Werkzeug's safe_join function allows path segments with Windows device names. On Windows, there are special device names such as CON, AUX, etc that are implicitly present and readable in every directory. 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 patched in version 3.1.4.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
Low
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.5% · higher than 43% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
WE
Werkzeug · Palletsprojects
before 3.1.4 · source: NVD
Affected product
WE
Werkzeug
Palletsprojects
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-66221
CVE.org
https://www.cve.org/CVERecord?id=CVE-2025-66221
Patch
https://github.com/pallets/werkzeug/commit/4b833376a45c323a189cd11d2362bcffdb1c0c13
Release Notes
https://github.com/pallets/werkzeug/releases/tag/3.1.4
Vendor Advisory
https://github.com/pallets/werkzeug/security/advisories/GHSA-hgf8-39gv-g3f2
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