CVE-2025-66168
Apache ActiveMQ is Vulnerable to Integer Overflow or Wraparound
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 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.
How to fix CVE-2025-66168
To remediate CVE-2025-66168, upgrade the affected package to a fixed version below.
- —upgrade to 5.19.2 or later
- —no fix listed
- —upgrade to 5.19.2 or later
- —upgrade to 5.19.2 or later
- —upgrade to 5.19.2 or later
Is CVE-2025-66168 being exploited?
Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.