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CVE-2026-109855

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

HIGH
7.5
CVSS Score
Published: October 15, 2026 at 08:12 AM UTC
Updated: October 19, 2026 at 08:46 PM UTC
2 products affected across 2 vendorsUndiciUndici

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Severity
HIGH7.5
Exploit prediction
EPSS 0.3%
SSVC
No known exploit

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.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

Undici· Node.jsnpm
95%
8.11.0 ≤ v < 8.11.2
Undici· Undici
90%
Vendor states this is fixed in 8.11.2 (unaffected)

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

Patch and advisory references

References (2)

MitigationVendor Advisory
Source: cverecord
https://github.com/nodejs/undici/security/advisories/GHSA-qq8j-7v2v-3rwp
Vendor Advisory
Source: cverecord
https://cna.openjsf.org/security-advisories.html

SSVC — Action Prioritization

SSVCNo known exploitAutomatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

7.5HIGHopenjs
Vector?

Quick Info

StatusANALYZED
CWE
CWE-248CWE-754

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