Arbitrary Counter Vulnerability in Bouncy Castle for Java
CVE-2026-59644

8.7HIGH

Key Information:

Vendor

Legion Of The Bouncy Castle Inc.

Status
Bc-java
Vendor
CVE Published:
3 August 2026

What is CVE-2026-59644?

The vulnerability in Bouncy Castle for Java affects the MLS hash-ratchet feature, allowing it to honor an arbitrary 32-bit generation counter provided by the sender. This could potentially lead to unforeseen ramifications for the integrity and confidentiality of messages being processed by the application. It is essential for users to upgrade to the latest version to mitigate risks associated with this issue.

Affected Version(s)

BC-JAVA all 1.73 < 1.85

References

https://github.com/bcgit/bc-java/wiki/CVE-2026-59644
vendor-advisory
https://github.com/bcgit/bc-java/commit/610d8757d855afe19...
patch

CVSS V4

Score:
8.7
Severity:
HIGH
Confidentiality:
None
Integrity:
None
Availability:
High
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
.