In mongoose built-in TLS < 7.23, a network attacker can impersonate a TLS server when the client uses a multi-cert CA bundle. In src/tls_builtin.c, mg_tls_init() leaves tls->ca_der.len as 0 while storing the bundle in tls->ca_bundle_der, and mg_tls_recv_cert() accepts a CN match via tls_bundle_find() without mg_tls_verify_cert_signature(). Upgrade to 7.23.