CVE-2026-59642 in Bouncy Castle for Java
Summary
by MITRE • 08/03/2026
In Bouncy Castle for Java before 1.85, CMS AuthenticatedData content not bound to MAC when authAttrs present. This issue also affects Bouncy Castle for Java LTS before 2.73.12, and Bouncy Castle for Java FIPS (BC-FJA) before bcpkix-fips 1.0.12 (1.0.X series), 2.0.12 (2.0.X series) and 2.1.12 (2.1.X series).
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Analysis
by VulDB Data Team • 08/03/2026
The vulnerability in Bouncy Castle for Java affects the CMS AuthenticatedData implementation where content is not properly bound to the Message Authentication Code when authenticated attributes are present. This represents a critical flaw in cryptographic message processing that undermines the integrity and authenticity guarantees of the CMS (Cryptographic Message Syntax) framework. The issue stems from improper handling of the binding between the content being authenticated and the MAC calculation, creating a potential attack vector for message tampering and authentication bypass scenarios.
This technical flaw falls under CWE-310 which addresses cryptographic weaknesses in the binding of data to authentication mechanisms. The vulnerability specifically impacts the CMS AuthenticatedData structure where authenticated attributes are used alongside content, but the cryptographic binding process fails to properly incorporate all relevant data elements into the MAC computation. This creates a situation where an attacker could potentially modify the content without detection, as the MAC would not reflect the actual content changes when authenticated attributes are present.
The operational impact of this vulnerability extends across multiple Bouncy Castle Java implementations including the standard Java version and the LTS releases, as well as the FIPS certified variants. Systems using any of these affected versions may be vulnerable to attacks where malicious actors could manipulate CMS messages containing authenticated attributes while maintaining valid signatures, leading to potential data integrity compromises and authentication failures in security-critical applications. The issue affects both the 1.0.X and 2.0.X series of BC-FJA FIPS implementations, indicating a widespread problem across different release branches.
The vulnerability relates to ATT&CK technique T1552.006 which involves the exploitation of cryptographic weaknesses in authentication mechanisms. Organizations relying on Bouncy Castle for secure communications, digital signatures, and encrypted message processing may face significant security risks if they have not upgraded to patched versions. This includes applications handling sensitive data such as healthcare records, financial transactions, government communications, and any systems requiring strong cryptographic integrity guarantees.
Mitigation strategies should prioritize immediate upgrading to the patched versions including Bouncy Castle Java 1.85, LTS 2.73.12, and the appropriate FIPS versions mentioned in the advisory. Organizations should conduct comprehensive vulnerability assessments of their systems using affected Bouncy Castle components and implement network monitoring to detect potential exploitation attempts. Additionally, security teams should review existing CMS message processing logic to identify any custom implementations that might be vulnerable due to improper handling of authenticated attributes or MAC binding procedures.