Stream-mode MAC Forgery Vulnerability in Bouncy Castle for Java
CVE-2026-12816

8.7HIGH

Key Information:

Vendor

Legion Of The Bouncy Castle Inc.

Status
Bc-java
Bc-lts-java
Vendor
CVE Published:
3 August 2026

What is CVE-2026-12816?

Bouncy Castle for Java versions prior to 1.85 are susceptible to a stream-mode MAC forgery vulnerability stemming from a length-dependent key derivation function (KDF) split issue in the IESEngine component. This vulnerability also impacts the long-term support (LTS) branch before version 2.73.12. Attackers could exploit this flaw to forge message authentication codes, potentially compromising the integrity and authenticity of encrypted communications.

Affected Version(s)

BC-JAVA all 0 < 1.85

BC-LTS-JAVA all 2.73.0 < 2.73.12

References

https://github.com/bcgit/bc-java/wiki/CVE-2026-12816
vendor-advisory
https://github.com/bcgit/bc-java/commit/6d9e4bbaee9409713...
patch

CVSS V4

Score:
8.7
Severity:
HIGH
Confidentiality:
None
Integrity:
High
Availability:
None
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Alex Gaynor in collaboration with Claude and Anthropic Research
.