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CVE PROGRAM SOURCE RECORD5.3 Medium

CVE-2026-9595

webpack-dev-server vulnerable to HMR WebSocket interception via permissive user proxies

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'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.

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

webpack-dev-server webpack-dev-server

Default version status: unaffected

  • 0 to < 5.2.5affected
  • 5.2.5unaffected
pkg:npm/webpack-dev-server

References