CVE-2026-123872

CVE-2026-123872 is a high-severity vulnerability rated 8.1/10 on the CVSS scale. A client certificate authentication bypass in Node.js TLS lets a client change the servername during TLS 1.2 renegotiation to reach endpoints it was not authorized for. On a server that applies different client-certificate policies per hostname, for example stricter admin-only client-cert auth on one host and ordinary client-cert auth on another, a client that authenticates for a permitted host can renegotiate the TLS 1.2 connection under a different servername and carry its existing authentication to the protected host, bypassing the stricter policy. EPSS estimates a 0.36% chance of exploitation in the next 30 days.