Is CVE-2025-66221 actively exploited?

CVE-2025-66221 has no public evidence of in-the-wild exploitation as of 2025-12-03.

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

CVE-2025-66221 has a CVSS score of 6.3 (MEDIUM severity). Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X.

How do I patch CVE-2025-66221?

Patch guidance is available from palletsprojects security advisories. CVEDatabase generates AI-assisted remediation guidance on demand for CVE-2025-66221.

Which products are affected by CVE-2025-66221?

1 product: palletsprojects werkzeug.

CVE-2025-66221 - remediation guidance & executive summary

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 Metrics

Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack Vector: network
Complexity: low
Privileges: none
User Action: none
Confidentiality: undefined
Integrity: undefined
Availability: undefined
Weaknesses: CWE-67

Metadata

Primary Vendor: PALLETSPROJECTS
Published: 11/29/2025
Last Modified: 12/3/2025
Source: NIST NVD
Note: Verify all details with official vendor sources before applying patches.

Affected Products

palletsprojects : werkzeug

Remediation Guidance

Executive Summary

Cite this page

CVE-2025-66221. CVEDatabase.com. Retrieved 1 May 2026. https://cvedatabase.com/cve/CVE-2025-66221

View on NIST NVD

CVE-2025-66221 vulnerability