CVE-2026-39304: Apache ActiveMQ Client, Apache ActiveMQ Broker, Apache ActiveMQ All, Apache ActiveMQ: Incorrect handling of TLSv1.3 KeyUpdate can be exploited to cause DoS via OOM

["Christopher L. Shannon" <cshannon () apache org>]

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