Severity: important 

Affected versions:

- Apache ActiveMQ Client (org.apache.activemq:activemq-client) before 5.19.4
- Apache ActiveMQ Client (org.apache.activemq:activemq-client) 6.0.0 before 
6.2.4
- Apache ActiveMQ Broker (org.apache.activemq:activemq-broker) before 5.19.4
- Apache ActiveMQ Broker (org.apache.activemq:activemq-broker) 6.0.0 before 
6.2.4
- Apache ActiveMQ All (org.apache.activemq:activemq-all) before 5.19.4
- Apache ActiveMQ All (org.apache.activemq:activemq-all) 6.0.0 before 6.2.4
- Apache ActiveMQ (org.apache.activemq:apache-activemq) before 5.19.4
- Apache ActiveMQ (org.apache.activemq:apache-activemq) 6.0.0 before 6.2.4

Description:

Denial of Service via Out of Memory vulnerability in Apache ActiveMQ Client, 
Apache ActiveMQ Broker, Apache ActiveMQ.

ActiveMQ NIO SSL transports do not correctly handle TLSv1.3 handshake 
KeyUpdates triggered by clients. This makes it possible for a client to rapidly 
trigger updates which causes the broker to exhaust all its memory in the SSL 
engine leading to DoS.

Note: TLS versions before TLSv1.3 (such as TLSv1.2) are broken but are not 
vulnerable to OOM. Previous TLS versions require a full handshake renegotiation 
which causes a connection to hang but not OOM. This is fixed as well.
This issue affects Apache ActiveMQ Client: before 5.19.4, from 6.0.0 before 
6.2.4; Apache ActiveMQ Broker: before 5.19.4, from 6.0.0 before 6.2.4; Apache 
ActiveMQ: before 5.19.4, from 6.0.0 before 6.2.4.

Users are recommended to upgrade to version 6.2.4 or 5.19.5, which fixes the 
issue.

References:

https://activemq.apache.org/
https://www.cve.org/CVERecord?id=CVE-2026-39304


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