CVE-2025-66221 is a medium-severity vulnerability affecting Werkzeug versions prior to 3.1.4, specifically when running on Microsoft Windows. The flaw in Werkzeug's safe_join function allows path segments with Windows device names, causing the send_from_directory function to hang indefinitely when attempting to open files with such names. This unauthenticated network-based attack has a low impact on availability, with no impact on confidentiality or integrity. There is currently no known active exploitation, public exploit code, or significant community discussion surrounding this vulnerability.
| Vendor | Product | Version(s) | CPE |
|---|---|---|---|
< 3.1.4CPE matchmatch criteria | cpe:2.3:a:palletsprojects:werkzeug:*:*:*:*:*:*:*:* |
CVSS version used by this source: 4.0
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
The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.1 Bluesky, 0.0 Mastodon, and 0.4 GitHub mentions.
No media coverage found for this CVE.
The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.
Werkzeug safe_join() allows Windows special device names
Dec 2, 2025Werkzeug: Werkzeug: Denial of service via Windows device names in path segments
Nov 29, 2025Werkzeug safe_join() allows Windows special device names
Nov 11, 2025