{"id":"GHSA-qq8j-7v2v-3rwp","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.","aliases":["CVE-2026-109855"],"modified":"2026-10-27T16:15:05.346335461Z","published":"2026-10-27T16:09:45Z","database_specific":{"nvd_published_at":"2026-10-15T09:17:16Z","cwe_ids":["CWE-248","CWE-754"],"severity":"HIGH","github_reviewed":true,"github_reviewed_at":"2026-10-27T16:09:45Z"},"references":[{"type":"WEB","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":"WEB","url":"https://cna.openjsf.org/security-advisories.html"},{"type":"PACKAGE","url":"https://github.com/nodejs/undici"},{"type":"WEB","url":"https://github.com/nodejs/undici/releases/tag/v8.11.2"}],"affected":[{"package":{"name":"undici","ecosystem":"npm","purl":"pkg:npm/undici"},"ranges":[{"type":"SEMVER","events":[{"introduced":"8.11.0"},{"fixed":"8.11.2"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/10/GHSA-qq8j-7v2v-3rwp/GHSA-qq8j-7v2v-3rwp.json"}}],"schema_version":"1.9.2","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"}]}