CVE-2026-9595 MEDIUM

CVE-2026-9595: webpack-dev-server vulnerable to HMR WebSocket interception via permissive user proxies

Vendor Webpack-Dev-Server
Product webpack-dev-server
Weakness CWE-346 · Origin validation
Published June 15, 2026
Last update June 15, 2026
View on NVD All CVEs

CVSS base score

5.3/10
Attack vector Network
Attack complexity Low
Privileges required None
User interaction None
Confidentiality None
Integrity None

CVSS vector

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

What the vulnerability does

01Description

Impact: When a user-configured proxy on webpack-dev-server has a broad context (e.g. /) and ws: true, it also intercepts the dev server's own HMR WebSocket and forwards it to the proxy target. This leaks the browser's cookies and Origin header to the backend, bypasses the dev server's Host/Origin validation, and corrupts the HMR socket (both HMR and the proxy end up writing to the same socket). Patches: Fixed in webpack-dev-server@5.2.5. Workarounds: Scope user-defined proxy context to specific paths instead of /, or omit ws: true from the proxy entry when WebSocket forwarding is not required.

Key dates

02Disclosure timeline

June 15, 2026 CVE published
June 15, 2026 Record updated