CVE-2025-66168

/// Technical description

WARNING:

Users of 6.x should upgrade to 6.2.4 or later as the fix was missed in previous 6.x releases.

See the  following for more details:

https://activemq.apache.org/security-advisories.data/CVE-2026-40046-announcement.txt

https://www.cve.org/CVERecord?id=CVE-2026-40046

Original Report:

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 affect

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References