CVE-2026-55856: MariaDB has cleartext password disclosure to a MITM on the initial-handshake

When a Java application connects with sslMode=verify-full (or verify-ca) and a password but does not pin a server certificate, Connector/J deliberately accepts an untrusted/self-signed certificate at the TLS layer (the “MITM-proof without a CA” feature) and proves the server’s identity afterwards by binding the certificate fingerprint into the authentication exchange. That fingerprint enforcement is applied to the OK-packet and auth-switch paths but not to the initial-handshake path. An active man-in-the-middle that presents a self-signed certificate, claims to be MariaDB, and names the initial authentication plugin mysql_clear_password receives the victim’s database password in cleartext, before any fingerprint/identity check runs. The connection is torn down a moment later, but the credential is already gone.