CVE-2026-59638

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

State: Published
Severity: 9.3 Critical
Published: Aug 3, 2026
Updated: Aug 3, 2026
Reserved: Jul 6, 2026

Description

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).

Scores

CVSS	Score	Vector	Source
4.0	9.3 Critical	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	bcorg

Weaknesses

CWE-297 Improper Validation of Certificate with Host Mismatch

Affected Products

Product	Versions
BC-JAVALegion of the Bouncy Castle Inc.	1.61 to before 1.85Affected
BC-LTS-JAVALegion of the Bouncy Castle Inc.	2.73.0 to before 2.73.12Affected
BC-FJALegion of the Bouncy Castle Inc.	1.0.7 to before 1.0.24Affected 2.0.0 to before 2.0.24Affected 2.1.0 to before 2.1.24Affected

References

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