CVE-2025-27533 describes a memory allocation with excessive size value vulnerability in Apache ActiveMQ. This vulnerability allows attackers to exploit improper validation of buffer size values during the unmarshalling of OpenWire commands. Consequently, this flaw can lead to excessive memory allocation, causing a denial of service (DoS) by depleting process memory, thereby affecting applications and services that rely on the availability of the ActiveMQ broker, especially when not using mutual TLS connections.
The vulnerability has a CVSS score of 6.9, indicating a medium severity level. It is critical for organizations that utilize ActiveMQ to understand the potential risks associated with this vulnerability, as it can disrupt service availability. Users are advised to upgrade to version 6.1.6+, 5.19.0+, 5.18.7+, 5.17.7, or 5.16.8 to mitigate the issue, since ActiveMQ 5.19.0 is not affected.
The urgency for defenders is clear: organizations should prioritize patching immediately to prevent exploitation. The vulnerability is not currently known to be actively exploited, but the existence of a public exploit increases the potential for future attacks.
Implementing mutual TLS as a workaround can help mitigate the risk for those unable to upgrade immediately. Organizations must remain vigilant and monitor for unusual activity that may indicate attempts to exploit this vulnerability.
Vulnerability Details
The vulnerability described in CVE-2025-27533 is categorized as a memory allocation with excessive size value vulnerability in Apache ActiveMQ. It is officially described as follows: During unmarshalling of OpenWire commands, the size value of buffers was not properly validated, which could lead to excessive memory allocation and be exploited to cause a denial of service (DoS).
This issue affects Apache ActiveMQ versions from 6.0.0 before 6.1.6, from 5.18.0 before 5.18.7, from 5.17.0 before 5.17.7, and before 5.16.8. ActiveMQ 5.19.0 is not affected. The vulnerability has a CVSS score of 6.9 (medium severity) and is classified under CWE-789.
The vulnerability was published on May 7, 2025, and its last modification date was November 3, 2025. The attack vector is classified as NETWORK, with a low attack complexity, and it requires high privileges to exploit.
Technical Analysis
The root cause of this vulnerability lies in the improper validation of the size value of buffers during the unmarshalling of OpenWire commands. Attackers may leverage this flaw by sending specially crafted commands to the affected ActiveMQ broker, which can trigger the excessive memory allocation.
The attack vector is network-based, meaning that an attacker does not need to have physical access to the server to exploit this vulnerability. The attack complexity is low, as the attacker requires high privileges and does not need user interaction to exploit the vulnerability.
The impact of successful exploitation can be significant, leading to high availability impact due to the denial of service. The confidentiality and integrity impacts are categorized as none, indicating that sensitive information is not directly compromised through this vulnerability.
Risk & Impact Analysis
The real-world deployment risk associated with CVE-2025-27533 is notable, particularly for organizations that rely heavily on Apache ActiveMQ for messaging and communication. The risk to organizations includes potential service disruptions due to denial of service attacks, which can significantly impact business operations.
With a CVSS score of 6.9, this vulnerability falls within the medium severity category, indicating an urgent need for remediation. Organizations should address this issue in their priority patch cycle to mitigate potential exploitation risks. The blast radius potential is concerning, as multiple services and applications relying on ActiveMQ can be affected.
Given that the vulnerability is known to have an exploit, organizations that fail to patch could find themselves at increased risk of service outages and operational issues. The urgency for patching is clear, as organizations should prioritize patching immediately.
Exploitation Status
Signal | Status |
|---|---|
Known Exploit | Yes |
Public PoC | Yes |
Actively Exploited | No |
Ransomware Use | No |
Affected Versions
The vulnerable versions of Apache ActiveMQ include: from 6.0.0 before 6.1.6, from 5.18.0 before 5.18.7, from 5.17.0 before 5.17.7, and before 5.16.8. ActiveMQ 5.19.0 is not affected. Users should ensure they are running versions 6.1.6+, 5.19.0+, 5.18.7+, 5.17.7, or 5.16.8 to mitigate this vulnerability.
Mitigation & Remediation
Organizations are advised to upgrade to the latest versions of Apache ActiveMQ to resolve this vulnerability. Specifically, upgrading to version 6.1.6+, 5.19.0+, 5.18.7+, 5.17.7, or 5.16.8 is recommended.
For those unable to upgrade immediately, implementing mutual TLS can act as a mitigation measure to protect affected brokers. It is also advisable to review configurations and apply hardening practices wherever applicable.
Organizations should monitor their ActiveMQ logs for unusual memory usage patterns that may indicate attempts to exploit this vulnerability. Additionally, ensuring that network controls are in place can help mitigate the risk of exploitation.
Penetration testing should be considered to validate the effectiveness of any remediation efforts.
Detection Guidance
To detect potential exploitation attempts, organizations should monitor logs for indicators such as unusual spikes in memory usage, unexpected process crashes, and irregular command patterns sent to the ActiveMQ broker.
Behavioral anomalies in network traffic, especially towards ActiveMQ endpoints, should be flagged for further investigation. Implementing network signatures can also aid in identifying exploitation attempts.
AppSecure Threat Intelligence Insight
The long-term significance of CVE-2025-27533 lies in its demonstration of the importance of robust validation checks in software development. Organizations must adopt secure coding practices to prevent similar vulnerabilities from being introduced.
The pattern represented by this vulnerability highlights the need for ongoing security assessments and proactive measures to enhance application resilience against denial of service attacks. Lessons learned from this incident can guide security teams in implementing comprehensive review processes.
Organizations should prioritize building a culture of security awareness and ensuring that development teams are trained in secure coding practices. For more insights, refer to our article on vulnerability management program design and consider adopting a framework for continuous security testing to reduce risks.
Strategic defensive takeaways include prioritizing timely updates, understanding the implications of vulnerabilities, and maintaining an adaptive security posture in the face of emerging threats. Focused efforts on enhancing application security can significantly reduce the attack surface.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
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