Vulnerability 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 [email protected]. 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.
CVSS Score
MEDIUM
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Webpack.Js | Webpack-Dev-Server | < 5.2.5 |
Related Weaknesses (CWE)
References
- https://cna.openjsf.org/security-advisories.htmlVendor Advisory
- https://github.com/facebook/create-react-app/pull/7444Issue TrackingPatch
- https://github.com/vuejs/vue-cli/commit/72ba7505aff2a8314e82aa5082379a77504a1fcbPatch
- https://github.com/webpack/webpack-dev-server/pull/4316Issue TrackingPatch
- https://github.com/webpack/webpack-dev-server/security/advisories/GHSA-mx8g-39q3MitigationVendor Advisory
FAQ
What is CVE-2026-9595?
CVE-2026-9595 is a vulnerability with a CVSS score of 5.3 (MEDIUM). 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 le...
How severe is CVE-2026-9595?
CVE-2026-9595 has been rated MEDIUM with a CVSS base score of 5.3/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-9595?
Check the references section above for vendor advisories and patch information. Affected products include: Webpack.Js Webpack-Dev-Server.