Is CVE-2025-66221 in the CISA KEV catalog?

No. CVE-2025-66221 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2025-66221?

CVE-2025-66221 has a CVSS v3 base score of 5.3 (Moderate).

What is the EPSS score for CVE-2025-66221?

CVE-2025-66221 has an EPSS score of 0.47% (37th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2025-66221?

Upgrade werkzeug to 3.1.4 or later.

CVE & CISA-KEV Catalog

CVE-2025-66221

MEDIUM

5.3

CVSS v3

NVD

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.

CWE-67

How to fix

Remediation Available

werkzeugNVD

Affected:< 3.1.4Fixed in:3.1.4CVE-2025-66221derived from NVD

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityNone

IntegrityNone

AvailabilityLow

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

Exploit Intelligence

0.47%probability of exploitation in 30 days

37thpercentile

Low risk: more likely to be exploited than 37% of all known CVEs.

References

Patch1

github.com

Vendor Advisory1

github.com

Release Notes1

github.com

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-12-03.