CVE-2026-59638: Bouncycastle Bc-Java

Medium severity, CVSS 6.5. EPSS: 0.3% chance of exploitation in the next 30 days.

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).

Affected products

• Bouncycastle Bc-Java: before 1.85 (fixed in 1.85)
• Bouncycastle Bctls-Fips: from 1.0.0, before 1.0.24 (fixed in 1.0.24); from 2.0.19, before 2.0.24 (fixed in 2.0.24); from 2.1.20, before 2.1.24 (fixed in 2.1.24)
• Bouncycastle Bouncy Castle For Java LTS: up to and including 2.73.11

Published 2026-08-03. Last modified 2026-08-28.