A silent threat has emerged, capable of bringing critical web applications to a screeching halt. For organizations relying on the ubiquitous Apache Struts 2 framework, this isn’t merely a hypothetical concern; it’s a stark reality. A recently discovered denial-of-service (DoS) vulnerability allows attackers to cripple servers, leading to significant service disruptions and potential data loss. Understanding this vulnerability and taking immediate action is paramount for maintaining operational continuity.

Understanding the Apache Struts 2 DoS Vulnerability (CVE-2025-64775)

The vulnerability, officially tracked as CVE-2025-64775, impacts multiple versions of the Apache Struts 2 web application framework. At its core, this critical flaw exploits a file leak during multipart request processing. In essence, when handling file uploads or other multipart data, a design oversight allows for an uncontrolled accumulation of temporary files or data on the server’s disk.

Attackers can leverage this mechanism to rapidly exhaust available disk space. By continuously sending specially crafted multipart requests, they can trigger an incessant write operation that eventually fills the server’s storage. Once the disk is full, the server becomes unresponsive, leading to a complete denial of service. This isn’t a complex remote code execution, but rather a straightforward resource exhaustion attack with potentially devastating consequences for the affected web applications.

Impact of Disk Exhaustion on Apache Struts 2 Servers

The implications of disk exhaustion extend far beyond a momentary inconvenience. When a server’s disk space is fully utilized, critical system processes, logging mechanisms, and application functionalities can no longer operate. This results in:

• Complete Server Crashes: The most immediate and severe consequence is the inability of the server to function, leading to a complete outage.
• Service Disruptions: Web applications hosted on the affected server become inaccessible, impacting end-users, business operations, and customer trust.
• Data Loss Potential: While not a direct data breach, data being processed at the time of the crash might be corrupted or lost if not properly committed.
• Performance Degradation: Even before full exhaustion, the server’s performance can degrade significantly as it struggles with limited resources.
• Reputational Damage: Prolonged outages can severely tarnish an organization’s reputation and lead to financial losses.

Affected Versions and Prioritization

While specific affected versions are often detailed in official Apache Struts advisories, the general recommendation is to assume your instance is vulnerable if you haven’t recently updated. Organizations are strongly advised to consult the official Apache Struts security bulletins for the precise list of vulnerable versions. Given the critical nature of this DoS vulnerability, patching should be treated as a high-priority incident response task.

Remediation Actions

Addressing CVE-2025-64775 requires prompt and decisive action. The primary remediation strategy involves upgrading to a patched version of Apache Struts 2.

• Upgrade Apache Struts 2: Immediately update your Apache Struts 2 installation to the latest stable version that addresses this vulnerability. Always refer to the official Apache Struts project website for release notes and upgrade instructions.
• Monitor Disk Usage: Implement robust monitoring solutions for disk space utilization on all servers running Apache Struts 2. Alerts should be configured to notify administrators well before critical thresholds are reached.
• Review Multipart Request Configurations: While upgrading is the definitive fix, reviewing and hardening configurations related to multipart request processing (e.g., maximum file sizes, temporary directory handling) can add an additional layer of defense.
• Implement Web Application Firewalls (WAFs): A properly configured WAF can help detect and block malicious multipart requests before they reach the Apache Struts 2 application.
• Regular Security Audits: Conduct frequent security audits and penetration tests to identify and rectify potential weaknesses in your web applications.

Tools for Detection and Mitigation

Tool Name	Purpose	Link
OWASP ZAP	General web application vulnerability scanning and penetration testing. Can help identify misconfigurations.	https://www.zaproxy.org/
Nessus	Comprehensive vulnerability scanner, often includes checks for known CVEs in web frameworks.	https://www.tenable.com/products/nessus
Snort / Suricata	Intrusion Detection/Prevention Systems (IDS/IPS) that can be configured with rules to detect suspicious multipart request patterns.	https://www.snort.org/ https://suricata-ids.org/
Prometheus / Grafana	Monitoring tools for server resource utilization, including disk space, critical for early detection of DoS attempts.	https://prometheus.io/ https://grafana.com/

Conclusion

The Apache Struts 2 DoS vulnerability (CVE-2025-64775) serves as a critical reminder of the ongoing need for vigilance in web application security. While seemingly simple, a disk exhaustion attack can have profound and immediate consequences for service availability. Prioritizing updates, implementing robust monitoring, and employing comprehensive security practices are essential steps to safeguard your infrastructure against this and similar threats. Proactive defense remains the most effective strategy against today’s evolving cyber landscape.