{"id":"GHSA-qq8j-7v2v-3rwp","aliases":["CVE-2026-109855"],"title":"undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake","description":"### 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upgrading.","severity":"high","score":7.5,"published":"2026-10-27T16:09:45.000Z","modified":"2026-10-27T16:15:05.346Z","withdrawn":false,"knownExploited":false,"affected":[{"ecosystem":"npm","name":"undici","ranges":[{"events":[{"introduced":"8.11.0"},{"fixed":"8.11.2"}],"type":"SEMVER"}],"versions":[],"fixed":["8.11.2"]}],"references":["https://github.com/nodejs/undici/security/advisories/GHSA-qq8j-7v2v-3rwp","https://nvd.nist.gov/vuln/detail/CVE-2026-109855","https://github.com/nodejs/undici/pull/5873","https://github.com/nodejs/undici/commit/dd28c5c55f4a25f7c441fd4365b1191f96c3b8bf","https://cna.openjsf.org/security-advisories.html","https://github.com/nodejs/undici","https://github.com/nodejs/undici/releases/tag/v8.11.2"],"sources":[{"name":"OSV","id":"GHSA-qq8j-7v2v-3rwp","modified":"2026-10-27T16:15:05.346335461Z","url":"https://osv.dev/vulnerability/GHSA-qq8j-7v2v-3rwp"}],"assessments":[{"source":"OSV","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5}]}