CVE-2026-12803 PUBLISHED

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

Assigner: bcorg
Reserved: 21.06.2026 Published: 03.08.2026 Updated: 03.08.2026

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.

Metrics

CVSS 4.0

CVSS 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
CVSS Score: 8.7

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	None	Confidentiality	None
Attack Complexity	Low	Integrity	High	Integrity	None
Attack Requirements	None	Availability	None	Availability	None
Privileges Required	None
User Interaction	None

CVSS 4.0

Product Status

Vendor	Legion of the Bouncy Castle Inc.
Product	BC-JAVA
Versions	Default: unaffected affected from 0 to 1.85 (excl.)

Vendor	Legion of the Bouncy Castle Inc.
Product	BC-LTS-JAVA
Versions	Default: unaffected affected from 2.73.0 to 2.73.12 (excl.)

CVE-2026-12803 PUBLISHED

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

Metrics

Product Status

Credits

References

Problem Types