undici HTTP client crash via TLS1.2 renegotiation (v4.2.18.12.1)
CVE-2026-87018 Published on October 15, 2026

undici vulnerable to Denial of Service via TLS 1.2 certificate-changing renegotiation
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.

NVD

Weakness Types

Uncaught Exception

An exception is thrown from a function, but it is not caught. When an exception is not caught, it may cause the program to crash or expose sensitive information.

What is an assertion failure Vulnerability?

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.

CVE-2026-87018 has been classified to as an assertion failure vulnerability or weakness.


Affected Versions

undici: