CVE-2026-9595: webpack-dev-server vulnerable to HMR WebSocket interception via permissive user proxies
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).
References
- cna.openjsf.org/security-advisories.html
- github.com/advisories/GHSA-mx8g-39q3-5c79
- github.com/facebook/create-react-app/pull/7444
- github.com/vuejs/vue-cli/commit/72ba7505aff2a8314e82aa5082379a77504a1fcb
- github.com/webpack/webpack-dev-server/pull/4316
- github.com/webpack/webpack-dev-server/security/advisories/GHSA-mx8g-39q3-5c79
- nvd.nist.gov/vuln/detail/CVE-2026-9595
Code Behaviors & Features
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