What is the CVSS score of CVE-2026-39304?

CVE-2026-39304 has a CVSS 3.1 base score of 7.5 (High). CVSS vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. EPSS exploitation probability: 0.0%.

Which versions of Apache Activemq Client are affected by CVE-2026-39304?

Apache ActiveMQ versions before 5.19.4 and 6.0.0-6.2.3 are vulnerable to unauthenticated remote denial of service attacks that exhaust broker memory through malformed TLSv1.3 handshake requests,…. A patch is available.

How to fix or mitigate CVE-2026-39304?

Within 24 hours: Identify all ActiveMQ deployments using versions <5.19.4 or 6.0.0-6.2.3 with NIO SSL transports enabled and assess business criticality. Within 7 days: Implement network-level controls (rate limiting, connection throttling on TLSv1.3 KeyUpdate requests) or disable NIO SSL transport if operationally feasible; apply compensating controls below. Within 30 days: Upgrade to ActiveMQ 5.19.4 or later (5.15.x/5.16.x/5.17.x/5.18.x not mentioned as patched-verify vendor advisories) or 6.2.4+ once released and tested.

Apache Activemq Client CVE-2026-39304

EUVD-2026-21362 HIGH

Uncontrolled Resource Consumption (CWE-400)

2026-04-10 apache

GHSA-5568-6qcg-g7fx

Apache Denial Of Service Apache Activemq Client Apache Activemq Broker Apache Activemq All Apache Activemq

7.5

CVSS 3.1 · Vendor: apache

Severity by source

Vendor (apache) PRIMARY

7.5 HIGH

AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Red Hat

7.5 HIGH

qualitative

Primary rating from Vendor (apache).

CVSS VectorVendor: apache

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Lifecycle Timeline

Patch released

Apr 11, 2026 - 02:30 nvd

Patch available

EUVD ID Assigned

Apr 10, 2026 - 11:00 euvd

EUVD-2026-21362

Analysis Generated

Apr 10, 2026 - 11:00 vuln.today

CVE Published

Apr 10, 2026 - 10:54 nvd

HIGH 7.5

Blast Radius

ecosystem impact

† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth

6 maven packages depend on org.apache.activemq:activemq-all (3 direct, 3 indirect)
21 maven packages depend on org.apache.activemq:activemq-broker (14 direct, 7 indirect)
31 maven packages depend on org.apache.activemq:activemq-client (8 direct, 23 indirect)

Ecosystem-wide dependent count for version 6.0.0 and other introduced versions.

DescriptionCVE.org

Denial of Service via Out of Memory vulnerability in Apache ActiveMQ Client, Apache ActiveMQ Broker, Apache ActiveMQ.

ActiveMQ NIO SSL transports do not correctly handle TLSv1.3 handshake KeyUpdates triggered by clients. This makes it possible for a client to rapidly trigger updates which causes the broker to exhaust all its memory in the SSL engine leading to DoS.

Note: TLS versions before TLSv1.3 (such as TLSv1.2) are broken but are not vulnerable to OOM. Previous TLS versions require a full handshake renegotiation which causes a connection to hang but not OOM. This is fixed as well. This issue affects Apache ActiveMQ Client: before 5.19.4, from 6.0.0 before 6.2.4; Apache ActiveMQ Broker: before 5.19.4, from 6.0.0 before 6.2.4; Apache ActiveMQ: before 5.19.4, from 6.0.0 before 6.2.4.

Users are recommended to upgrade to version 6.2.4 or 5.19.5, which fixes the issue.

AnalysisAI

Out-of-memory denial of service in Apache ActiveMQ allows unauthenticated remote attackers to exhaust broker memory via rapid TLSv1.3 KeyUpdate requests. Affects ActiveMQ Client, Broker, and All distributions versions <5.19.4 and 6.0.0-6.2.3 when NIO SSL transports are used. Vulnerability arises from improper handling of TLSv1.3 handshake KeyUpdate messages, enabling clients to trigger unbounded memory allocation in the SSL engine. No public exploit identified at time of analysis. CVSS 7.5 (AV:N/AC:L/PR:N) indicates network-accessible, low-complexity attack requiring no authentication.

Technical ContextAI

Root cause stems from CWE-400 uncontrolled resource consumption in NIO SSL transport layer. TLSv1.3 KeyUpdate mechanism permits clients to repeatedly trigger cryptographic key rotation without full handshake overhead. ActiveMQ's SSL engine allocates memory per update without rate limiting or bounds checking, creating unbounded heap growth. Pre-TLSv1.3 protocols require full renegotiation causing connection hang but not OOM.

RemediationAI

Vendor-released patches: upgrade to Apache ActiveMQ version 6.2.4 or 5.19.5 immediately. These releases implement proper bounds checking and rate limiting for TLSv1.3 KeyUpdate handling in NIO SSL transports. For environments unable to upgrade immediately, mitigate by disabling TLSv1.3 protocol support at the broker configuration level and restrict to TLSv1.2, though this introduces connection hang risk during renegotiation. Alternatively, disable NIO SSL transport and use alternative transport protocols. Monitor heap memory utilization for abnormal growth patterns. Complete advisory and upgrade instructions: https://activemq.apache.org/security-advisories.data/CVE-2026-39304-announcement.txt