A significant security vulnerability has been identified in Apache ActiveMQ, a widely utilized open-source message broker. This flaw, designated as CVE-2025-27533, allows remote attackers to induce a Denial of Service (DoS) condition by exploiting improper memory allocation during the processing of OpenWire commands. Such an exploit can lead to unexpected service disruptions, posing substantial risks to organizations that depend on ActiveMQ for real-time messaging.
Understanding the Vulnerability
The core issue lies in the inadequate validation of buffer sizes during the unmarshalling of OpenWire commands. Specifically, the BaseDataStreamMarshaller class’s looseUnmarshalByteSequence method fails to properly check the size of incoming data. This oversight permits attackers to request excessive memory allocation, potentially exhausting system resources and causing the ActiveMQ broker to crash. Even with maxFrameSize configuration limits in place, the vulnerability remains exploitable, as initial size checks may pass, but subsequent evaluations can still allow for overly large memory allocations.
Affected Versions
The vulnerability impacts the following versions of Apache ActiveMQ:
– 6.0.0 to 6.1.5
– 5.18.0 to 5.18.6
– 5.17.0 to 5.17.6
– 5.16.0 to 5.16.7
Notably, versions 5.19.0 and later are not affected.
Potential Impact
Exploitation of CVE-2025-27533 can lead to:
– Service Disruption: The ActiveMQ broker may crash, leading to downtime and operational interruptions.
– Resource Exhaustion: Excessive memory allocation can deplete system resources, affecting overall performance.
– Operational Risks: Organizations relying on ActiveMQ for critical messaging services may experience significant business impacts due to service outages.
Mitigation Strategies
To address this vulnerability, organizations should:
1. Upgrade ActiveMQ: Immediately update to the patched versions:
– 6.1.6 or later
– 5.19.0 or later
– 5.18.7
– 5.17.7
– 5.16.8
2. Implement Mutual TLS: For those unable to upgrade promptly, enforcing mutual Transport Layer Security (TLS) can mitigate the risk, as the exploit is ineffective when mutual TLS connections are required.
3. Monitor and Audit: Regularly review system logs and monitor for unusual memory usage patterns that may indicate exploitation attempts.
4. Restrict Access: Limit network access to the ActiveMQ broker to trusted clients and networks to reduce exposure.
Conclusion
The discovery of CVE-2025-27533 underscores the critical importance of rigorous input validation, especially when handling serialized data from untrusted sources. Organizations utilizing Apache ActiveMQ should promptly assess their systems, apply the necessary updates, and implement recommended security measures to safeguard their messaging infrastructure against potential DoS attacks.
