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CVE-2026-109855

7.5 · HIGH

undici is an HTTP client library for Node.js.

Published Oct 15, 2026nodejsCWE-248EPSS 0.28%

Overview

CVE-2026-109855 is a high-severity vulnerability affecting nodejs undici. It was published on October 15, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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

Check the references section for vendor advisories and patches from nodejs. Update undici to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected products

VendorProductVersionsStatus
nodejsundici>= 8.11.0, < 8.11.2Affected

References

Refcna.openjsf.org/security-advisories.htmlGitHubgithub.com/nodejs/undici/security/advisories/GHSA-qq8j-7v2v-3rwp

How CyberStrike helps

Frequently asked questions

What is CVE-2026-109855?

CVE-2026-109855 is a high-severity vulnerability affecting nodejs undici. It was published on October 15, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-109855?

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-109855?

Check the references section for vendor advisories and patches from nodejs. Update undici to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-109855?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-109855 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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