CVE-2026-59644 MLS hash-ratchet honours arbitrary 32-bit generation counter from sender
A flaw in the Bouncy Castle Java library allows a sender to manipulate the MLS hash-ratchet generation counter, potentially disrupting secure messaging protocols.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-59644?
CVE-2026-59644 is a high-severity vulnerability in Bouncycastle Bc-Java, published on 3 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In Bouncy Castle for Java before 1.85, MLS hash-ratchet honours arbitrary 32-bit generation counter from sender.
Weakness: CWE-834
Which versions are affected by CVE-2026-59644?
It affects 1 product.
Products include Bouncycastle Bc-Java.
How do I fix CVE-2026-59644?
Upgrade to a fixed version.
Is CVE-2026-59644 being exploited?
There is no known exploitation of CVE-2026-59644 in the wild and no public exploit code.
Other vulnerabilities in Bouncycastle Bc-Java
- CVE-2007-6721 Legion of the Bouncy Castle Java Cryptography API Bleichenbacher Oracle Vulnerability
- CVE-2018-1000613 Deserialization of Untrusted Data in Bouncy castle
- CVE-2026-58062 Stapled OCSP response accepted without binding to the checked certificate
- CVE-2026-59638 JSSE hostname verifier CN-fallback enabled by default despite documented opt-in
- CVE-2026-59650 MTI/A0 DH agreement exponentiates unvalidated peer value
Sources
Also known as DEBIAN-CVE-2026-59644, GHSA-xrmp-pcg8-5q9v, UBUNTU-CVE-2026-59644.