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CVE-2026-40046: Apache ActiveMQ, Apache ActiveMQ All, Apache ActiveMQ MQTT: Missing fix for CVE-2025-66168: MQTT control packet remaining length field is not properly validated

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-09 · updated 2026-10-26
• Weakness: CWE-190

Description

Integer Overflow or Wraparound vulnerability in Apache ActiveMQ, Apache ActiveMQ All, Apache ActiveMQ MQTT. The fix for "CVE-2025-66168: MQTT control packet remaining length field is not properly validated" was only applied to 5.19.2 (and future 5.19.x) releases but was missed for all 6.0.0+ versions. This issue affects Apache ActiveMQ: from 6.0.0 before 6.2.4; Apache ActiveMQ All: from 6.0.0 before 6.2.4; Apache ActiveMQ MQTT: from 6.0.0 before 6.2.4. Users are recommended to upgrade to version 6.2.4 or a 5.19.x version starting with 5.19.2 or later (currently latest is 5.19.5), which fixes the issue.

Affected products

• Apache ActiveMQ: from 6.0.0 before 6.2.4 — fixed in 6.2.4
• Apache Software Foundation Apache ActiveMQ All: from 6.0.0 before 6.2.4 — fixed in 6.2.4
• Apache Software Foundation Apache ActiveMQ MQTT: from 6.0.0 before 6.2.4 — fixed in 6.2.4

How to fix

Upgrade to a fixed version: Apache ActiveMQ 6.2.4; Apache Software Foundation Apache ActiveMQ All 6.2.4; Apache Software Foundation Apache ActiveMQ MQTT 6.2.4. Check the vendor advisory for mitigations.

References

• https://activemq.apache.org/security-advisories.data/CVE-2026-40046-announcement.txt
• https://lists.apache.org/thread/zdntj5rcgjjzrpow84o339lzldy68zrg
• https://www.cve.org/CVERecord?id=CVE-2025-66168

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