CVE-2026-12803
Received Received - Intake

Bouncy Castle Java KCCMBlockCipher MAC Nonce Binding Flaw

Publication date: 2026-08-03

Last updated on: 2026-08-03

Assigner: bcorg

Description
In Bouncy Castle for Java before 1.85, KCCMBlockCipher MAC does not bind nonce when AAD is absent (cross-nonce AEAD forgery). This issue also affects Bouncy Castle for Java LTS before 2.73.12.

CVSS Scores

EPSS Scores

Probability:
Percentile:

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-2026-12803
EUVD
EUVD-2026-52134

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
CWE Icon
KEV
KEV Icon
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

AI Quick Actions

Instant insights powered by AI
Executive Summary

This vulnerability in Bouncy Castle for Java before 1.85 involves the KCCMBlockCipher MAC not binding the nonce when AAD (Additional Authenticated Data) is absent. This allows for cross-nonce AEAD forgery, meaning an attacker could manipulate encrypted data without detection.

Detection Guidance

This vulnerability affects Bouncy Castle for Java before 1.85 and Bouncy Castle for Java LTS before 2.73.12. Detection requires checking the installed version of Bouncy Castle libraries in your Java applications. Use commands like 'mvn dependency:tree' or 'gradle dependencies' to inspect project dependencies. Look for versions below 1.85 or 2.73.12 respectively.

Impact Analysis

If you use Bouncy Castle for Java before 1.85 or Bouncy Castle for Java LTS before 2.73.12, this vulnerability could allow attackers to forge encrypted messages, potentially leading to unauthorized data access or tampering with sensitive information.

Compliance Impact

This vulnerability could compromise data integrity and confidentiality, which are critical for compliance with GDPR and HIPAA. Failure to address it may result in non-compliance, potential legal penalties, and reputational damage.

Mitigation Strategies

Upgrade Bouncy Castle for Java to version 1.85 or later and Bouncy Castle for Java LTS to version 2.73.12 or later. Remove or replace any instances of KCCMBlockCipher in your codebase. Review cryptographic configurations to ensure proper nonce binding when AAD is absent.

Chat Assistant

Ask questions about this CVE
Hi! I’m here to help you understand CVE-2026-12803. Ask me anything about the vulnerability, its impact, or mitigation strategies.
0/70

EPSS Chart