Vulnerability in Webpack-Dev-Server
CVE-2026-9595
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.
EPSS exploit prediction
EPSS: 0.002 (12.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 13th percentile — 12.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.002 · change: +0.001
Affected products
- Webpack-Dev-Server — versions 0, 5.2.5
- Webpack.js Webpack-Dev-Server
Weakness classification (CWE)
References
- ce714d77-add3-4f53-aff5-83d477b104bb (Mitigation, Vendor Advisory)
- ce714d77-add3-4f53-aff5-83d477b104bb (Vendor Advisory)
- ce714d77-add3-4f53-aff5-83d477b104bb (Patch, Issue Tracking)
- ce714d77-add3-4f53-aff5-83d477b104bb (Patch)
- ce714d77-add3-4f53-aff5-83d477b104bb (Patch, Issue Tracking)
Frequently asked questions
- What is CVE-2026-9595?
- CVE-2026-9595 is a medium-severity vulnerability in Webpack-Dev-Server, classified under Origin Validation Error. CVSS score: 5.3/10. Published 2026-06-15.
- How severe is CVE-2026-9595?
- Medium severity. CVSS v3 base score is 5.3 out of 10.