CVE-2026-59638 PUBLISHED

JSSE hostname verifier CN-fallback enabled by default despite documented opt-in

Assigner: bcorg
Reserved: 06.07.2026 Published: 03.08.2026 Updated: 03.08.2026

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).

Metrics

CVSS Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/U:Amber
CVSS Score: 9.3

Product Status

Vendor Legion of the Bouncy Castle Inc.
Product BC-JAVA
Versions Default: unaffected
  • affected from 1.61 to 1.85 (excl.)
Vendor Legion of the Bouncy Castle Inc.
Product BC-LTS-JAVA
Versions Default: unaffected
  • affected from 2.73.0 to 2.73.12 (excl.)
Vendor Legion of the Bouncy Castle Inc.
Product BC-FJA
Versions Default: unaffected
  • affected from 1.0.7 to 1.0.24 (excl.)
  • affected from 2.0.0 to 2.0.24 (excl.)
  • affected from 2.1.0 to 2.1.24 (excl.)

Credits

  • Alex Gaynor in collaboration with Claude and Anthropic Research reporter

References

Problem Types

  • CWE-297 Improper Validation of Certificate with Host Mismatch CWE