CVE-2026-9595

Summary

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 Software

VendorProductVersion RangeStatus
webpack-dev-serverwebpack-dev-server0 < 5.2.5affected
webpack-dev-serverwebpack-dev-server5.2.5unaffected

Weaknesses

  • CWE-346: CWE-346: Origin Validation Error
  • CWE-441: CWE-441: Unintended Proxy or Intermediary ('Confused Deputy')

ADP Enrichment

CISA ADP Vulnrichment

  • SSVC:
  • Exploitation: none
    • Automatable: yes
    • Technical Impact: partial

References