CVE-2026-59638: JSSE hostname verifier CN-fallback enabled by default despite documented opt-in

Affects Bouncy Castle for Java FIPS (BC-FJA) bctls-fips before 1.0.24 (1.0.X series), 2.0.24 (2.0.X series) and 2.1.24 (2.1.X series). HostnameUtil gates the fallback that matches the certificate CN when no dNSName SAN is present on a property whose unset default the code treats as enabled, contrary to its documentation. Because name-constraint processing only constrains SAN entries of the constrained type, a leaf with no dNSName SAN passes a dNSName-constrained chain, and the verifier then matches the attacker-chosen CN against the target hostname.