CVE-2025-66168

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.

The most popular and powerful open source messaging and Integration Patterns server.

Security Fix(es):

A vulnerability classified as problematic has been found in Apache ActiveMQ (Application Server Software).CWE is classifying the issue as 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 can introduce other weaknesses when the calculation is used for resource management or execution control.This is going to have an impact on integrity, and availability.Upgrading to version 5.19.2, 6.1.9 or 6.2.1 eliminates this vulnerability.(CVE-2025-66168)

The most popular and powerful open source messaging and Integration Patterns server.

Security Fix(es):

A vulnerability classified as problematic has been found in Apache ActiveMQ (Application Server Software).CWE is classifying the issue as 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 can introduce other weaknesses when the calculation is used for resource management or execution control.This is going to have an impact on integrity, and availability.Upgrading to version 5.19.2, 6.1.9 or 6.2.1 eliminates this vulnerability.(CVE-2025-66168)

The most popular and powerful open source messaging and Integration Patterns server.

Security Fix(es):

A vulnerability classified as problematic has been found in Apache ActiveMQ (Application Server Software).CWE is classifying the issue as 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 can introduce other weaknesses when the calculation is used for resource management or execution control.This is going to have an impact on integrity, and availability.Upgrading to version 5.19.2, 6.1.9 or 6.2.1 eliminates this vulnerability.(CVE-2025-66168)

The most popular and powerful open source messaging and Integration Patterns server.

Security Fix(es):

A vulnerability classified as problematic has been found in Apache ActiveMQ (Application Server Software).CWE is classifying the issue as 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 can introduce other weaknesses when the calculation is used for resource management or execution control.This is going to have an impact on integrity, and availability.Upgrading to version 5.19.2, 6.1.9 or 6.2.1 eliminates this vulnerability.(CVE-2025-66168)

The most popular and powerful open source messaging and Integration Patterns server.

Security Fix(es):

A vulnerability classified as problematic has been found in Apache ActiveMQ (Application Server Software).CWE is classifying the issue as 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 can introduce other weaknesses when the calculation is used for resource management or execution control.This is going to have an impact on integrity, and availability.Upgrading to version 5.19.2, 6.1.9 or 6.2.1 eliminates this vulnerability.(CVE-2025-66168)

The most popular and powerful open source messaging and Integration Patterns server.

Security Fix(es):

A vulnerability classified as problematic has been found in Apache ActiveMQ (Application Server Software).CWE is classifying the issue as 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 can introduce other weaknesses when the calculation is used for resource management or execution control.This is going to have an impact on integrity, and availability.Upgrading to version 5.19.2, 6.1.9 or 6.2.1 eliminates this vulnerability.(CVE-2025-66168)

The most popular and powerful open source messaging and Integration Patterns server.

Security Fix(es):

A vulnerability classified as problematic has been found in Apache ActiveMQ (Application Server Software).CWE is classifying the issue as 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 can introduce other weaknesses when the calculation is used for resource management or execution control.This is going to have an impact on integrity, and availability.Upgrading to version 5.19.2, 6.1.9 or 6.2.1 eliminates this vulnerability.(CVE-2025-66168)

The most popular and powerful open source messaging and Integration Patterns server.

Security Fix(es):

A vulnerability classified as problematic has been found in Apache ActiveMQ (Application Server Software).CWE is classifying the issue as 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 can introduce other weaknesses when the calculation is used for resource management or execution control.This is going to have an impact on integrity, and availability.Upgrading to version 5.19.2, 6.1.9 or 6.2.1 eliminates this vulnerability.(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.

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.

Root has patched CVE-2025-66168 in the io.root.org.apache.activemq:activemq-mqtt package for Root:Maven. Multiple fixed versions available.