CVE-2026-12803

KCCMBlockCipher MAC does not bind nonce when AAD is absent (cross-nonce AEAD forgery)

Published Aug 3, 2026 CVSS 4.0 · 8.7 High EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
First Time appeared Bouncycastle
Bouncycastle bc-java
Bouncycastle bouncy Castle For Java Lts
CPEs cpe:2.3:a:bouncycastle:bc-java:*:*:*:*:*:*:*:*
cpe:2.3:a:bouncycastle:bouncy_castle_for_java_lts:*:*:*:*:*:*:*:*
Vendors & Products Bouncycastle
Bouncycastle bc-java
Bouncycastle bouncy Castle For Java Lts
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N'}

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Legion Of The Bouncy Castle Inc.
Legion Of The Bouncy Castle Inc. bc-java
Legion Of The Bouncy Castle Inc. bc-lts-java
Vendors & Products Legion Of The Bouncy Castle Inc.
Legion Of The Bouncy Castle Inc. bc-java
Legion Of The Bouncy Castle Inc. bc-lts-java
Type Values Removed Values Added
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.
Title KCCMBlockCipher MAC does not bind nonce when AAD is absent (cross-nonce AEAD forgery)
Weaknesses CWE-354
References
Metrics cvssV4_0

{'score': 8.7, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/U:Amber'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
bcorg
Published
Updated
Aug 3, 2026, 3:22 PM
Reserved
Jun 21, 2026, 1:50 AM
Status
Analyzed
Published
Aug 3, 2026, 4:16 AM
Modified
Sep 2, 2026, 2:37 PM