CVE-2026-109855

undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake

Published Oct 15, 2026 CVSS 3.1 · 7.5 High EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-qq8j-7v2v-3rwp undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake
History
Type Values Removed Values Added
First Time appeared Nodejs
Nodejs undici
CPEs cpe:2.3:a:nodejs:undici:*:*:*:*:*:node.js:*:*
Vendors & Products Nodejs
Nodejs undici
Type Values Removed Values Added
First Time appeared Undici
Undici undici
Vendors & Products Undici
Undici undici
Type Values Removed Values Added
Metrics ssvc

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

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

Weaknesses

Sources

Status
PUBLISHED
Assigner
openjs
Published
Updated
Oct 15, 2026, 2:22 PM
Reserved
Oct 13, 2026, 7:28 AM
Status
Analyzed
Published
Oct 15, 2026, 9:17 AM
Modified
Oct 19, 2026, 8:46 PM
Severity
Important
Public date
Oct 15, 2026, 8:12 AM