CVE-2026-59638
CriticalCVSS 9.3Summary
In Bouncy Castle for Java before 1.85, the JSSE hostname verifier enables CN-fallback by default despite documented opt-in. This issue also affects LTS and FIPS versions.
Risk Assessment
An attacker could exploit this to perform phishing or man-in-the-middle attacks, as a certificate with a matching CN (but incorrect SAN) may be accepted.
Recommendation
Upgrade Bouncy Castle to version 1.85 or later (for the regular version), to 2.73.12 or later (for LTS), and to the appropriate FIPS versions.
Original NVD description (English source)
In Bouncy Castle for Java before 1.85, JSSE hostname verifier CN-fallback enabled by default despite documented opt-in. This issue also affects Bouncy Castle for Java LTS before 2.73.12, and Bouncy Castle for Java FIPS (BC-FJA) before bctls-fips 1.0.24 (1.0.X series), 2.0.24 (2.0.X series) and 2.1.24 (2.1.X series).