CVE-2025-66221

Q: How do I fix CVE-2025-66221?

Upgrade werkzeug to 3.1.4 or later.

Q: Is CVE-2025-66221 being actively exploited?

Not that we know of. CVE-2025-66221 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.52% is the estimated probability that it will be exploited in the next 30 days. That is higher than 41% of all scored CVEs.

Q: How severe is CVE-2025-66221?

CVE-2025-66221 has a CVSS v3 base score of 5.3, rated moderate. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

Q: What does CVE-2025-66221 affect?

Published advisories record a fix for werkzeug (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

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

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

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

0.52%probability of exploitation in 30 days

41stpercentile

Moderate risk: more likely to be exploited than 41% of all known CVEs.

References

Patch1

github.com

Vendor Advisory1

github.com

Release Notes1

github.com

Related Vulnerabilities

Other CWE-67 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2024-51745	Critical	10.0	0.8%	-	Fix
CVE-2026-27199	Medium	5.3	0.6%	-	Fix
CVE-2024-35197	Medium	5.4	0.4%	-	-
CVE-2026-21860	Medium	5.3	0.4%	-	Fix

Common questions

How do I fix CVE-2025-66221?

Upgrade werkzeug to 3.1.4 or later.

Is CVE-2025-66221 being actively exploited?

Not that we know of. CVE-2025-66221 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.52% is the estimated probability that it will be exploited in the next 30 days. That is higher than 41% of all scored CVEs.

How severe is CVE-2025-66221?

CVE-2025-66221 has a CVSS v3 base score of 5.3, rated moderate. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2025-66221 affect?

Published advisories record a fix for werkzeug (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

Embed a live status badge for CVE-2025-66221

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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.