CVE-2026-12816
Received Received - Intake

Bouncy Castle Java MAC Forgery via KDF Split

Publication date: 2026-08-03

Last updated on: 2026-08-03

Assigner: bcorg

Description
In Bouncy Castle for Java before 1.85, IESEngine stream-mode MAC forgery via length-dependent KDF split. This issue also affects Bouncy Castle for Java LTS before 2.73.12.

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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-2026-12816
EUVD
EUVD-2026-52135

Affected Vendors & Products

Showing 2 associated CPEs
Vendor Product Version / Range
bouncy_castle bouncy_castle_for_java to 1.85 (exc)
bouncy_castle bouncy_castle_for_java_lts to 2.73.12 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-354 The product does not validate or incorrectly validates the integrity check values or "checksums" of a message. This may prevent it from detecting if the data has been modified or corrupted in transmission.

Attack-Flow Graph

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Executive Summary

This vulnerability in Bouncy Castle for Java before 1.85 allows for MAC forgery in stream-mode IESEngine due to a length-dependent Key Derivation Function (KDF) split. It also affects Bouncy Castle for Java LTS before 2.73.12.

Detection Guidance

Detection requires checking the version of Bouncy Castle for Java in use. Commands like 'find / -name "bouncycastle*.jar" 2>/dev/null' or 'mvn dependency:tree | grep bouncycastle' can help identify the library version. If the version is below 1.85 (or 2.73.12 for LTS), the system is vulnerable.

Impact Analysis

An attacker could exploit this to forge message authentication codes (MACs), potentially allowing unauthorized data tampering or spoofing in applications using vulnerable versions of Bouncy Castle for Java.

Compliance Impact

This vulnerability could lead to data integrity breaches, which may violate compliance requirements for GDPR (data integrity principles) and HIPAA (integrity and security of protected health information).

Mitigation Strategies

Upgrade Bouncy Castle for Java to version 1.85 or later. For LTS versions, upgrade to 2.73.12 or later. Remove any outdated or vulnerable versions of the library from your system or project dependencies.

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