Vulnerability in Bouncycastle Bc-Java
CVE-2026-59638
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).
EPSS: 0.002 (11.4th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.
Affected products
- Bouncycastle Bc-java
- Bouncycastle Bctls-fips
- Bouncycastle Bouncy_castle_for_java_lts
- Legion Of The Bouncy Castle Inc. Bc-fja — versions 1.0.7, 2.0.0, 2.1.0
- Legion Of The Bouncy Castle Inc. Bc-java — versions 1.61
- Legion Of The Bouncy Castle Inc. Bc-lts-java — versions 2.73.0
Weakness classification (CWE)
References
- 91579145-5d7b-4cc5-b925-a0262ff19630 (Patch, patch)
- 91579145-5d7b-4cc5-b925-a0262ff19630 (Patch, patch)
- 91579145-5d7b-4cc5-b925-a0262ff19630 (vendor-advisory)
- 91579145-5d7b-4cc5-b925-a0262ff19630 (vendor-advisory, Third Party Advisory)
Frequently asked questions
- What is CVE-2026-59638?
- CVE-2026-59638 is a medium-severity vulnerability in Bouncycastle Bc-Java, classified under Improper Validation of Certificate with Host Mismatch. CVSS score: 6.5/10. Published 2026-08-03.
- How severe is CVE-2026-59638?
- Medium severity. CVSS v3 base score is 6.5 out of 10.