{"id":"CVE-2026-109855","state":"PUBLISHED","title":"undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake","description":"undici is an HTTP client library for Node.js. In versions 8.11.0 and 8.11.1, its experimental WebSocket client, which is enabled by default when HTTP/2 is allowed, mishandles a failed WebSocket handshake over HTTP/2: the request is already marked completed, so the abort becomes a no-op and the underlying HTTP/2 stream is left open with no error listener. When a malicious server then destroys the connection, the orphaned stream emits an unhandled error and the Node.js process exits. A remote, unauthenticated server can therefore crash any client that opens a WebSocket to it over HTTP/2, resulting in a denial of service. The issue is fixed in undici 8.11.2, and users should upgrade to 8.11.2 or later. As a workaround, set allowH2 to false to disable HTTP/2 for WebSocket connections, or avoid opening WebSocket connections to untrusted servers.","publishedAt":"2026-10-15T08:12:51.245Z","updatedAt":"2026-10-15T14:22:28.644Z","severity":{"score":7.5,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","source":"openjs"},"assigner":"openjs","products":["undici undici"],"affected":[{"vendor":"undici","product":"undici","packageURL":"pkg:npm/undici","defaultStatus":"unaffected","versions":[{"version":"8.11.0","status":"affected","lessThan":"8.11.2","versionType":"semver"},{"version":"8.11.2","status":"unaffected","versionType":"semver"}]}],"references":["https://github.com/nodejs/undici/security/advisories/GHSA-qq8j-7v2v-3rwp","https://cna.openjsf.org/security-advisories.html"],"weaknesses":["CWE-248","CWE-754"],"ingestedAt":"2026-10-29T20:10:33.477Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/109xxx/CVE-2026-109855.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-109855","state":"PUBLISHED","datePublished":"2026-10-15T08:12:51.245Z","dateUpdated":"2026-10-15T14:22:28.644Z","assignerShortName":"openjs","assignerOrgId":"ce714d77-add3-4f53-aff5-83d477b104bb","dateReserved":"2026-10-13T07:28:59.621Z"},"containers":{"cna":{"title":"undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake","descriptions":[{"lang":"en","value":"undici is an HTTP client library for Node.js. In versions 8.11.0 and 8.11.1, its experimental WebSocket client, which is enabled by default when HTTP/2 is allowed, mishandles a failed WebSocket handshake over HTTP/2: the request is already marked completed, so the abort becomes a no-op and the underlying HTTP/2 stream is left open with no error listener. When a malicious server then destroys the connection, the orphaned stream emits an unhandled error and the Node.js process exits. A remote, unauthenticated server can therefore crash any client that opens a WebSocket to it over HTTP/2, resulting in a denial of service. The issue is fixed in undici 8.11.2, and users should upgrade to 8.11.2 or later. As a workaround, set allowH2 to false to disable HTTP/2 for WebSocket connections, or avoid opening WebSocket connections to untrusted servers."}],"affected":[{"vendor":"undici","product":"undici","packageURL":"pkg:npm/undici","defaultStatus":"unaffected","versions":[{"version":"8.11.0","status":"affected","lessThan":"8.11.2","versionType":"semver"},{"version":"8.11.2","status":"unaffected","versionType":"semver"}]}],"references":[{"url":"https://github.com/nodejs/undici/security/advisories/GHSA-qq8j-7v2v-3rwp"},{"url":"https://cna.openjsf.org/security-advisories.html"}],"metrics":[{"format":"CVSS","cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","baseScore":7.5,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-248","lang":"en","description":"CWE-248: Uncaught Exception","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-754","lang":"en","description":"CWE-754: Improper Check for Unusual or Exceptional Conditions","type":"CWE"}]}],"providerMetadata":{"shortName":"openjs","orgId":"ce714d77-add3-4f53-aff5-83d477b104bb","dateUpdated":"2026-10-15T08:12:51.245Z"},"credits":[{"lang":"en","type":"reporter","value":"kjsik11"},{"lang":"en","type":"remediation developer","value":"mcollina"},{"lang":"en","type":"remediation reviewer","value":"jasnell"},{"lang":"en","type":"remediation reviewer","value":"metcoder95"},{"lang":"en","type":"remediation verifier","value":"UlisesGascon"},{"lang":"en","type":"remediation reviewer","value":"ronag"}],"x_generator":{"engine":"cve-kit 1.0.0"}},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-10-15T14:21:59.498708Z","id":"CVE-2026-109855","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-15T14:22:28.644Z"}}]}}}