How severe is CVE-2025-66221?

CVE-2025-66221 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.

Is CVE-2025-66221 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (38th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2025-66221?

CVE-2025-66221 affects Palletsprojects Werkzeug. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2025-66221?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2025-66221 have an EU (EUVD) identifier?

Yes. CVE-2025-66221 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-199893.

When was CVE-2025-66221 published?

CVE-2025-66221 was published on 2025-11-29 and last updated on 2026-06-17.

CVE-2025-66221

CVE-2025-66221 is a medium-severity vulnerability in Palletsprojects Werkzeug with a CVSS 3.x base score of 5.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-67.

Key facts

Severity: Medium (CVSS 3.x base score 5.3)
CVSS v4: 6.3
EPSS exploit prediction: 0% (38th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-199893
Weakness: CWE-67
Affected product: Palletsprojects Werkzeug
Published: 2025-11-29
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2025-66221?: 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.
How severe is CVE-2025-66221?: CVE-2025-66221 has a CVSS 3.x base score of 5.3, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.
Is CVE-2025-66221 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (38th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-66221?: CVE-2025-66221 affects Palletsprojects Werkzeug. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2025-66221?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2025-66221 have an EU (EUVD) identifier?: Yes. CVE-2025-66221 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-199893.
When was CVE-2025-66221 published?: CVE-2025-66221 was published on 2025-11-29 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:palletsprojects:werkzeug:*:*:*:*:*:*:*:*

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