---
id: CVE-2026-109855
title: undici is an HTTP client library for Node.js
summary: >-
  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
  alrea…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-248
  - CWE-754
vendor: undici
product: undici
affected:
  - undici >= 8.11.0 < 8.11.2
published: '2026-10-15'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T09:17:16.573'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-109855'
references:
  - url: 'https://cna.openjsf.org/security-advisories.html'
    label: ce714d77-add3-4f53-aff5-83d477b104bb
  - url: 'https://github.com/nodejs/undici/security/advisories/GHSA-qq8j-7v2v-3rwp'
    label: ce714d77-add3-4f53-aff5-83d477b104bb
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-109855.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-109855'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2553103'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-109855'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-109855'
tags:
  - nvd
  - cve.org
  - csaf
  - vex
  - red-hat
ingestedAt: '2026-10-15T08:58:33.102Z'
---

## Overview

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

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Vendor advisories

- **Red Hat VEX** · Important · affected: Cryostat 4, Exploit Intelligence, Red Hat AMQ Broker 7, Red Hat Ansible Automation Platform 2, Red Hat Build of Podman Desktop, Red Hat Developer Hub, … · no fix planned: Secrets Management Console for Red Hat OpenShift, Cryostat 4, Exploit Intelligence, Red Hat AMQ Broker 7, … · updated 2026-10-15 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-109855.json)