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.

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History

Thu, 15 Oct 2026 15:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Thu, 15 Oct 2026 13:30:00 +0000

Type Values Removed Values Added
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.
Title undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake
Weaknesses CWE-248
CWE-754
References
Metrics threat_severity

None

cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Important


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cve-icon MITRE

Status: PUBLISHED

Assigner: openjs

Published:

Updated: 2026-10-15T14:22:28.644Z

Reserved: 2026-10-13T07:28:59.621Z

Link: CVE-2026-109855

cve-icon Vulnrichment

Updated: 2026-10-15T14:22:23.478Z

cve-icon NVD

Status : Received

Published: 2026-10-15T09:17:16.573

Modified: 2026-10-15T15:17:28.083

Link: CVE-2026-109855

cve-icon Redhat

Severity : Important

Publid Date: 2026-10-15T08:12:51Z

Links: CVE-2026-109855 - Bugzilla

cve-icon OpenCVE Enrichment

No data.

Weaknesses