CVE-2026-59638
Received Received - Intake

JSSE Hostname Verifier CN-Fallback in Bouncy Castle Java

Publication date: 2026-08-03

Last updated on: 2026-08-03

Assigner: bcorg

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).

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Meta Information

Published
2026-08-03
Last Modified
2026-08-03
Generated
2026-08-03
AI Q&A
2026-08-03
EPSS Evaluated
N/A
NVD
CVE-2026-59638
EUVD
EUVD-2026-52016

Affected Vendors & Products

Showing 5 associated CPEs
Vendor Product Version / Range
bouncy_castle bouncy_castle to 1.85 (exc)
bouncy_castle bouncy_castle_lts to 2.73.12 (exc)
bouncy_castle bouncy_castle_fips to 1.0.24 (exc)
bouncy_castle bouncy_castle_fips to 2.0.24 (exc)
bouncy_castle bouncy_castle_fips to 2.1.24 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-297 The product communicates with a host that provides a certificate, but the product does not properly ensure that the certificate is actually associated with that host.

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Executive Summary

This vulnerability in Bouncy Castle for Java versions before 1.85 and related releases enables JSSE hostname verifier CN-fallback by default. This means the system may incorrectly verify hostnames using Common Name (CN) fields in SSL/TLS certificates instead of the more secure Subject Alternative Name (SAN) fields, even when this behavior is documented as opt-in.

Detection Guidance

This vulnerability involves JSSE hostname verifier CN-fallback being enabled by default in Bouncy Castle for Java. Detection requires checking the Bouncy Castle version in use. Commands like 'mvn dependency:tree' for Maven projects or inspecting the JAR manifest files can help identify affected versions (before 1.85, 2.73.12, or BC-FJA series).

Impact Analysis

This vulnerability could allow attackers to bypass hostname verification in SSL/TLS connections. This might lead to man-in-the-middle attacks where sensitive data transmitted over encrypted connections could be intercepted or altered without detection.

Compliance Impact

This vulnerability may violate compliance requirements for secure data transmission in GDPR and HIPAA. It undermines encryption integrity, potentially exposing personal or health data to unauthorized access, which could result in regulatory penalties and loss of trust.

Mitigation Strategies

Upgrade Bouncy Castle for Java to version 1.85 or later, Bouncy Castle LTS to 2.73.12 or later, and BC-FJA to bctls-fips 1.0.24, 2.0.24, or 2.1.24 depending on your series. Disable CN-fallback hostname verification if enabled.

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