CVE-2026-87018

Received Received - Intake

TLS 1.2 Renegotiation Crash in Undici

Publication date: 2026-10-15

Last updated on: 2026-10-15

Assigner: openjs

Description

undici is an HTTP client library for Node.js. In versions 4.2.1 through 6.29.0, 7.0.0 through 7.30.0, and 8.0.0 through 8.12.1, the client process crashes when a TLS 1.2 server renegotiates after the connection is established and presents a different, CA-trusted certificate whose hostname does not match the requested host. Node.js re-runs hostname verification on the renegotiated handshake and destroys the socket with a certificate-altname error, but undici's established-socket error handler asserted that this error code could never occur, so the peer-controlled error became an uncaught assertion that terminates the Node.js process, affecting both the HTTP/1.1 and HTTP/2 paths. A malicious or compromised HTTPS endpoint reached through undici or the global fetch() can crash the client with a single server-initiated renegotiation, taking down all in-flight requests and background work in the process, and exploitation needs no CA compromise because the attacker controls the endpoint and can present two ordinary valid certificates. Only TLS 1.2 is affected, since TLS 1.3 does not support renegotiation. The issue is fixed in undici 6.29.1, 7.30.1, and 8.12.2, and users should upgrade to one of those versions or later. As a workaround, restrict outbound connections to TLS 1.3 so renegotiation cannot occur, when the target endpoints support it.

CVSS Scores

EPSS Scores

Probability:
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Meta Information

Published

2026-10-15

Last Modified

2026-10-15

Generated

2026-10-16

AI Q&A

2026-10-16

EPSS Evaluated

N/A

NVD

CVE-2026-87018

EUVD

EUVD-2026-102318

Affected Vendors & Products

Vendor	Product	Version / Range
undici	undici	4.2.1
undici	undici	7.0.0
undici	undici	8.0.0

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-248	An exception is thrown from a function, but it is not caught.
CWE-617	The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.

Attack-Flow Graph

Executive Summary

This vulnerability affects the undici HTTP client library for Node.js. When a TLS 1.2 server renegotiates the connection after it is established and presents a different certificate that does not match the requested host, the client crashes due to an uncaught assertion error. This happens because undici's error handler incorrectly assumes this error cannot occur.

Detection Guidance

Detection involves checking the undici library version in use. Commands like 'npm list undici' or 'npm ls undici' can verify if the installed version falls within the vulnerable range (4.2.1-6.29.0, 7.0.0-7.30.0, 8.0.0-8.12.1). Monitor Node.js application logs for unexpected crashes during TLS renegotiation events.

Impact Analysis

A malicious or compromised HTTPS endpoint can crash your Node.js application by triggering a single renegotiation, causing all in-flight requests and background tasks to fail. This can disrupt services relying on undici or the global fetch() function.

Mitigation Strategies

Upgrade undici to version 6.29.1 or later, 7.30.1 or later, or 8.12.2 or later. As a temporary workaround, enforce TLS 1.3 for outbound connections if the target endpoints support it to prevent renegotiation.

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