CVE-2026-39304

Description

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.

How to fix CVE-2026-39304

To remediate CVE-2026-39304, upgrade the affected package to a fixed version below.

• —upgrade to 5.19.4 or later
• —no fix listed
• —upgrade to 5.19.4 or later
• —upgrade to 5.19.4 or later
• —upgrade to 5.19.4 or later
• —upgrade to 5.19.4 or later

Is CVE-2026-39304 being exploited?

Low — EPSS is 0.1%, meaning exploitation activity has not been observed at scale.

Affected packages (6)

• from 0, < 5.19.4, >= 6.0.0, < 6.2.4
• from 0
• from 0, < 5.19.4
• from 0, < 5.19.4
• from 0, < 5.19.4
• from 0, < 5.19.4

CVSS scores

References (5)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2026-39304
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2026-39304
• PATCHgithub.com/apache/activemq
• WEBactivemq.apache.org/security-advisories.data/CVE-2026-39304-announcement.txt