CVE-2025-66168
Received Received - Intake
Integer Overflow in Apache ActiveMQ MQTT Remaining Length Parsing

Publication date: 2026-03-04

Last updated on: 2026-04-10

Assigner: Apache Software Foundation

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.
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Meta Information
Published
2026-03-04
Last Modified
2026-04-10
Generated
2026-06-16
AI Q&A
2026-03-04
EPSS Evaluated
2026-06-14
NVD
CVE-2025-66168
EUVD
EUVD-2025-208266
Affected Vendors & Products
Showing 3 associated CPEs
Vendor Product Version / Range
apache activemq to 5.19.2 (exc)
apache activemq 6.2.0
apache activemq From 6.0.0 (inc) to 6.1.8 (inc)
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-190 The product performs a calculation that can produce an integer overflow or wraparound when the logic assumes that the resulting value will always be larger than the original value. This occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may become a very small or negative number.
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Executive Summary

This vulnerability in Apache ActiveMQ involves improper validation of the Remaining Length field during the decoding of malformed MQTT packets. An integer overflow can occur, causing the broker to miscalculate the total Remaining Length and misinterpret the payload as multiple MQTT control packets. This leads to unexpected behavior when the broker interacts with non-compliant clients and violates the MQTT v3.1.1 specification.

Impact Analysis

The vulnerability can cause Apache ActiveMQ brokers to behave unexpectedly when processing MQTT packets from non-compliant clients. This may lead to incorrect handling of messages after authentication, potentially disrupting communication or causing instability in the message broker service.

Compliance Impact

I don't know

Detection Guidance

I don't know

Mitigation Strategies

To mitigate this vulnerability, users are recommended to upgrade Apache ActiveMQ to version 5.19.2, 6.1.9, or 6.2.1, which contain fixes for this issue.

Note that brokers not enabling MQTT transport connectors are not impacted by this vulnerability.

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