Integer overflow in Apache Activemq
CVE-2025-66168
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.
Vulnerability class: Integer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N.
EPSS exploit prediction
EPSS: 0.008 (54.1th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 54th percentile — 54.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.008 · newest: 0.008 · change: 0.000
Affected products
- Apache Activemq — versions 6.2.0
- Apache Software Foundation Activemq — versions 0, 6.0.0, 6.2.0
- Apache Software Foundation Activemq All Module — versions 0, 6.0.0, 6.2.0
- Apache Software Foundation Activemq Mqtt Module — versions 0, 6.0.0, 6.2.0
Weakness classification (CWE)
References
- lists.apache.org/thread/13n8mkrb2jf2y6yyhpgrkmpqcm7djyto (vendor-advisory, Mailing List, Vendor Advisory)
- www.cve.org/CVERecord (related)
- activemq.apache.org/security-advisories.data/CVE-2026-40046-announcement.txt (related)
- af854a3a-2127-422b-91ae-364da2661108 (Mailing List, Third Party Advisory)
Frequently asked questions
- What is CVE-2025-66168?
- CVE-2025-66168 is a medium-severity vulnerability in Apache Activemq, classified under Integer Overflow or Wraparound. CVSS score: 5.4/10. Published 2026-03-04.
- How severe is CVE-2025-66168?
- Medium severity. CVSS v3 base score is 5.4 out of 10.