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

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-59638
StatePUBLISHED
Assignerbcorg
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-03 01:16:43 UTC
Updated2026-08-04 14:50:12 UTC
DescriptionIn 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).

Risk And Classification

Primary CVSS: v4.0 9.3 CRITICAL from 91579145-5d7b-4cc5-b925-a0262ff19630

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber

EPSS: 0.002760000 probability, percentile 0.198360000 (date 2026-08-04)

Problem Types: CWE-297 | CWE-297 CWE-297 Improper Validation of Certificate with Host Mismatch

VersionSourceTypeScoreSeverityVector
4.091579145-5d7b-4cc5-b925-a0262ff19630Secondary9.3CRITICALCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/C...
4.0CNACVSS9.3CRITICALCVSS: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 v4.0 Breakdown

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Confidentiality
High
Integrity
High
Availability
None
Sub Conf.
None
Sub Integrity
None
Sub Availability
None

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Legion Of The Bouncy Castle Inc. BC-JAVA affected 1.61 1.85 maven all
CNA Legion Of The Bouncy Castle Inc. BC-LTS-JAVA affected 2.73.0 2.73.12 maven all
CNA Legion Of The Bouncy Castle Inc. BC-FJA affected 1.0.7 1.0.24 maven all
CNA Legion Of The Bouncy Castle Inc. BC-FJA affected 2.0.0 2.0.24 maven all
CNA Legion Of The Bouncy Castle Inc. BC-FJA affected 2.1.0 2.1.24 maven all

References

ReferenceSourceLinkTags
github.com/bcgit/bc-java/commit/5ac55351cd1a8a7184d41c96a7ee87df0770240a 91579145-5d7b-4cc5-b925-a0262ff19630 github.com
github.com/bcgit/bc-java/commit/799bd15320a6310a447863638aa3df64acef829b 91579145-5d7b-4cc5-b925-a0262ff19630 github.com
github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9059638 91579145-5d7b-4cc5-b925-a0262ff19630 github.com
github.com/bcgit/bc-java/wiki/CVE-2026-59638 MITRE github.com
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Alex Gaynor in collaboration with Claude and Anthropic Research (en)

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