TLS certificate hostname bypass when the IP is written fullwidth digits

Summary

A flaw in Node.js TLS hostname verification allows a certificate without a matching IP address SAN to authenticate a connection to an IPv4 address when the host is written with non-ASCII characters, such as fullwidth digits (１２７.0.0.1).

tls.checkServerIdentity() did not recognize such hosts as IP addresses, even though they normalize and resolve to a regular IPv4 address, and matched them against the certificate DNS names and Common Name instead. A certificate containing DNS:127.0.0.1 or DNS:*.0.0.1 could therefore be accepted for an IP endpoint it was not issued for. This is a regression introduced after the fix for CVE-2026-48618.

This vulnerability affects Node.js 26.x and 24.x.