A Critical Flaw in Apache Struts: Understanding Disk Exhaustion Attacks

The digital landscape is a constant battlefield, and a recently discovered critical security vulnerability in Apache Struts has once again highlighted the persistent threat of denial-of-service (DoS) attacks. This flaw, which could allow attackers to trigger debilitating disk exhaustion attacks, has serious implications for the availability and stability of affected systems. For IT professionals, security analysts, and developers relying on Apache Struts, understanding this vulnerability and implementing timely remediation is paramount.

Apache Struts, a widely used open-source framework for developing Java EE web applications, is a cornerstone for many enterprises. A vulnerability of this nature in such a foundational component can have far-reaching consequences, potentially bringing critical services to a standstill and impacting business continuity. Let’s delve into the specifics of this flaw and what it means for your infrastructure.

CVE-2025-64775: The Root of the Disk Exhaustion Problem

The vulnerability, officially tracked as CVE-2025-64775, stems from a subtle but critical file leak within Apache Struts’ multipart request processing mechanism. Multipart requests are commonly used for handling file uploads in web applications. During this process, especially with large or numerous uploaded files, temporary files are often created and then, ideally, deleted once processing is complete.

However, the identified flaw in Struts prevents these temporary files from being properly cleaned up under certain conditions. This oversight allows an attacker to repeatedly send specially crafted multipart requests, leading to a continuous accumulation of unreleased files on the server’s disk. Over time, this uncontrolled file growth can rapidly consume all available disk space, culminating in a complete disk exhaustion scenario.

How Disk Exhaustion Leads to Denial of Service

A disk exhaustion attack is a potent form of denial of service. When a server’s disk space is fully utilized, the operating system and applications within it can no longer perform critical functions such as:

• Writing logs
• Creating temporary files for internal operations
• Saving new data
• Swapping memory to disk (virtual memory)

In essence, the system becomes choked, unable to process new requests or even maintain existing connections. This leads to:

• Application crashes and unavailability
• Slow performance and unresponsiveness
• Loss of data integrity (if write operations fail mid-process)
• Difficulty in system administration or troubleshooting due to log file failures

For organizations relying on Apache Struts for their public-facing or internal applications, a successful disk exhaustion attack can result in significant operational disruption, reputational damage, and potential financial losses.

Remediation Actions

Addressing CVE-2025-64775 is crucial for maintaining the resilience and availability of your Apache Struts applications. Immediate action is recommended:

• Upgrade Apache Struts: The primary and most effective remediation is to upgrade to the latest patched version of Apache Struts. Always refer to the official Apache Struts security advisories for the precise versions that contain the fix. Prioritizing updates ensures you benefit from the latest security improvements.
• Implement Input Validation and Size Limits: While upgrading is essential, robust input validation practices can act as a secondary defense. Configure your application to impose strict limits on the size and number of files that can be uploaded via multipart requests. This can help mitigate the immediate impact of an attack even before a full patch is applied.
• Monitor Disk Usage: Proactive monitoring of disk space on your Apache Struts servers is vital. Implement alerting mechanisms that notify administrators when disk usage exceeds predefined thresholds. This early warning can provide crucial time to respond before a complete disk exhaustion occurs.
• Review Application Logs: Regularly review application and server logs for suspicious activity, particularly repeated or unusually large multipart requests originating from a single source or IP address. Anomalous patterns can indicate an ongoing attack.
• Web Application Firewall (WAF) Rules: Consider implementing WAF rules to detect and block malicious multipart requests. A well-configured WAF can provide an additional layer of protection by filtering out known attack patterns.

Tools for Detection and Mitigation

Leveraging the right tools can significantly aid in identifying vulnerabilities and monitoring for potential attacks related to multipart processing and disk exhaustion.

Tool Name	Purpose	Link
Apache Struts Security Bulletins	Official advisories for vulnerabilities and patches.	https://struts.apache.org/security/
OWASP ZAP	Vulnerability scanner for web applications, can detect misconfigurations and some DoS vectors.	https://owasp.org/www-project-zap/
Nessus	Comprehensive vulnerability scanner, including web application and infrastructure scanning.	https://www.tenable.com/products/nessus
Prometheus + Grafana	Monitoring stack for collecting and visualizing server metrics, including disk utilization.	https://prometheus.io/
Web Application Firewalls (WAFs)	Network perimeter defense for blocking malicious web traffic (e.g., ModSecurity).	https://modsecurity.org/

Protecting Your Apache Struts Applications

The discovery of CVE-2025-64775 serves as a stark reminder that even well-established frameworks can harbor critical vulnerabilities. Proactive security measures, including diligent patching, robust input validation, and continuous monitoring, are indispensable. By understanding the mechanisms behind disk exhaustion attacks and implementing the recommended remediation steps, organizations can significantly bolster the resilience of their Apache Struts applications against such threats. Stay informed, stay vigilant, and ensure your systems are protected against the evolving landscape of cyber risks.