CVE-2025-66168: Apache ActiveMQ, Apache ActiveMQ All Module, Apache ActiveMQ MQTT Module: MQTT control packet remaining length field is not properly validated

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

Severity: 

Affected versions:

- Apache ActiveMQ (org.apache.activemq:apache-activemq) before 5.19.2
- Apache ActiveMQ (org.apache.activemq:apache-activemq) 6.0.0 before 6.1.9
- Apache ActiveMQ (org.apache.activemq:apache-activemq) 6.2.0 before 6.2.1
- Apache ActiveMQ All Module (org.apache.activemq:activemq-all) before 5.19.2
- Apache ActiveMQ All Module (org.apache.activemq:activemq-all) 6.0.0 before 6.1.9
- Apache ActiveMQ All Module (org.apache.activemq:activemq-all) 6.2.0 before 6.2.1
- Apache ActiveMQ MQTT Module (org.apache.activemq:activemq-mqtt) before 5.19.2
- Apache ActiveMQ MQTT Module (org.apache.activemq:activemq-mqtt) 6.0.0 before 6.1.9
- Apache ActiveMQ MQTT Module (org.apache.activemq:activemq-mqtt) 6.2.0 before 6.2.1

Description:

Apache ActiveMQ does not properly validate the remaining length field which may lead to an overflow during the decoding 
of malformed packets. When this integer overflow occurs, ActiveMQ may incorrectly compute the total Remaining Length 
and subsequently misinterpret the payload as multiple MQTT control packets which makes the broker susceptible to 
unexpected behavior when interacting with non-compliant clients. This behavior violates the MQTT v3.1.1 specification, 
which restricts Remaining Length to a maximum of 4 bytes. The scenario occurs on established connections after the 
authentication process. Brokers that are not enabling mqtt transport connectors are not impacted.

This issue affects Apache ActiveMQ: before 5.19.2, 6.0.0 to 6.1.8, and 6.2.0

Users are recommended to upgrade to version 5.19.2, 6.1.9, or 6.2.1, which fixes the issue.

Credit:

Gai Tanaka <641.work123 () gmail com> (finder)

References:

https://activemq.apache.org/
https://www.cve.org/CVERecord?id=CVE-2025-66168