{"id":"CVE-2026-9595","aliases":["GHSA-mx8g-39q3-5c79"],"url":"https://o3.security/vulnerability/CVE-2026-9595","summary":"webpack-dev-server vulnerable to HMR WebSocket interception via permissive user proxies","details":"### Impact\n\nWhen 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).\n\n### Patches\n\nFixed in `webpack-dev-server` 5.2.5.\n\n### Workarounds\n\nScope user-defined proxy `context` to specific paths instead of `/`, or omit `ws: true` from the proxy entry when WebSocket forwarding is not required.","published":"2026-06-15T15:00:21.488Z","modified":"2026-10-21T03:00:21.186691655Z","cvss":{"score":5.3,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"},"epss":{"score":0.00163,"percentile":0.05905,"asOf":"2026-09-17"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"webpack-dev-server","fixedVersion":"5.2.5"}],"fix":{"url":"https://github.com/facebook/create-react-app/pull/7444","label":"facebook/create-react-app#7444"},"references":[{"type":"ADVISORY","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/9xxx/CVE-2026-9595.json"},{"type":"ADVISORY","url":"https://github.com/webpack/webpack-dev-server/security/advisories/GHSA-mx8g-39q3-5c79"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-9595"},{"type":"FIX","url":"https://github.com/facebook/create-react-app/pull/7444"},{"type":"FIX","url":"https://github.com/vuejs/vue-cli/commit/72ba7505aff2a8314e82aa5082379a77504a1fcb"},{"type":"FIX","url":"https://github.com/webpack/webpack-dev-server/pull/4316"},{"type":"PACKAGE","url":"https://github.com/webpack/webpack-dev-server"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-21T03:00:21.186691655Z"}}