CVE-2026-39304
HIGHCVE-2026-39304 is a high-severity (CVSS 7.5) vulnerability in org.apache.activemq:activemq-client. O3 Security confirms whether CVE-2026-39304 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Apache ActiveMQ Client, Apache ActiveMQ Broker, Apache ActiveMQ All, Apache ActiveMQ: Incorrect handling of TLSv1.3 KeyUpdate can be exploited to cause DoS via OOM
Real-World Exposure
org.apache.activemq:activemq-client☕org.apache.activemq:activemq-client☕org.apache.activemq:activemq-broker☕org.apache.activemq:activemq-broker☕org.apache.activemq:activemq-all☕org.apache.activemq:activemq-all☕org.apache.activemq:apache-activemq☕org.apache.activemq:apache-activemqReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Maven packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.apache.activemq:activemq-client | all versions | 5.19.4 |
| ☕Maven | org.apache.activemq:activemq-client | ≥ 6.0.0&&< 6.2.4 | 6.2.4 |
| ☕Maven | org.apache.activemq:activemq-broker | all versions | 5.19.4 |
| ☕Maven | org.apache.activemq:activemq-broker | ≥ 6.0.0&&< 6.2.4 | 6.2.4 |
| ☕Maven | org.apache.activemq:activemq-all | all versions | 5.19.4 |
| ☕Maven | org.apache.activemq:activemq-all | ≥ 6.0.0&&< 6.2.4 | 6.2.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for org.apache.activemq:activemq-client. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update org.apache.activemq:activemq-client to 5.19.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-39304 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-39304 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-39304. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-39304 in your dependencies?
O3 detects CVE-2026-39304 across Maven dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.