CVE-2026-9595

Severity CVSS v4.0:

Pending analysis

Type:

Unavailable / Other

Publication date:

15/06/2026

Last modified:

16/06/2026

Description

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&#39;s own HMR WebSocket and forwards it to the proxy target. This leaks the browser&#39;s cookies and Origin header to the backend, bypasses the dev server&#39;s Host/Origin validation, and corrupts the HMR socket (both HMR and the proxy end up writing to the same socket).<br /> <br /> Patches: Fixed in webpack-dev-server@5.2.5.<br /> <br /> 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.

Impact

Vector 3.x

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L CVSS v3.1 Severity and Metrics:

Base Score: 5.30 MEDIUM
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Attack Vector (AV): Network
Attack Complexity (AC): Low
Privileges Required (PR): None
User Interaction (UI): None
Scope (S): Unchanged
Confidentiality (C): None
Integrity (I): None
Availability (A): Low