CVE-2026-109855: nodejs undici Uncaught Exception

Vulnerability summary

CVE-2026-109855 is a high (CVSS 7.5) Uncaught Exception vulnerability in nodejs undici. EPSS estimates a 0.28% chance of exploitation in the next 30 days, higher than 19% of scored vulnerabilities.

Timeline

1. 15-10-2026
   PublishedVulnerability first disclosed.
2. 15-10-2026
   Last modifiedVulnerability information updated.

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.

• CWE-248Uncaught ExceptionAn exception is thrown from a function, but it is not caught.
• CWE-754Improper Check for Unusual or Exceptional ConditionsThe product does not check or incorrectly checks for unusual or exceptional conditions that are not expected to occur frequently during day to day operation of the product.