{"id":"CVE-2026-109855","aliases":["GHSA-qq8j-7v2v-3rwp"],"url":"https://o3.security/vulnerability/CVE-2026-109855","summary":"undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake","details":"### Impact\n\nundici's experimental WebSocket client (enabled by default via `allowH2: true`) crashes the Node.js process when it connects to a malicious server over HTTP/2. If the server answers the WebSocket upgrade with a response that fails handshake validation, undici aborts the request, but the abort is a no-op because the request is already marked completed, so the underlying `ClientHttp2Stream` is left open with no error listener. When the server then destroys the connection, the orphaned stream emits an unhandled `error` and the process exits. A remote, unauthenticated server can therefore deny service to any client that opens a WebSocket to it over HTTP/2. undici 8.11.0 and 8.11.1 are affected; the regression was introduced in 8.11.0.\n\n### Patches\n\nUpgrade to `8.11.2`.\n\n### Workarounds\n\nSet `allowH2: false` to disable HTTP/2 for WebSocket connections, or avoid opening WebSocket connections to untrusted servers, until upgrading.","published":"2026-10-15T08:12:51.245Z","modified":"2026-10-28T02:30:44.506969006Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"npm","name":"undici","fixedVersion":"8.11.2"}],"fix":{"url":"https://github.com/nodejs/undici/pull/5873","label":"nodejs/undici#5873"},"references":[{"type":"ADVISORY","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/109xxx/CVE-2026-109855.json"},{"type":"ADVISORY","url":"https://github.com/nodejs/undici/security/advisories/GHSA-qq8j-7v2v-3rwp"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-109855"},{"type":"WEB","url":"https://github.com/nodejs/undici/pull/5873"},{"type":"WEB","url":"https://github.com/nodejs/undici/commit/dd28c5c55f4a25f7c441fd4365b1191f96c3b8bf"},{"type":"PACKAGE","url":"https://github.com/nodejs/undici"},{"type":"WEB","url":"https://github.com/nodejs/undici/releases/tag/v8.11.2"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-28T02:30:44.506969006Z"}}