CVE-2025-52520 is an integer overflow vulnerability classified under CWE-190 that affects Apache Tomcat versions from 8.5.0 through 11.0.8, including some milestone and maintenance releases. The flaw arises in the multipart upload handling code where certain unlikely configurations allow an integer overflow or wraparound to occur. This overflow can bypass the intended size limits on uploads, enabling an attacker to send excessively large payloads that the server fails to properly restrict. As a result, the server can be overwhelmed, leading to a denial of service (DoS) condition by exhausting memory or other resources. The vulnerability is exploitable remotely without requiring authentication or user interaction, increasing its risk profile. Although no known exploits are currently reported in the wild, the presence of a public CVE and the availability of fixed versions necessitate prompt action. The issue affects multiple major branches of Apache Tomcat, including 8.5.x, 9.0.x, 10.1.x, and 11.0.x, reflecting the widespread use of this server in enterprise environments. The Apache Software Foundation has addressed the vulnerability in versions 11.0.9, 10.1.43, and 9.0.107, recommending users upgrade to these or later versions to mitigate the risk.

For European organizations, the primary impact of CVE-2025-52520 is the potential for denial of service attacks that can disrupt critical web applications and services hosted on Apache Tomcat servers. This can lead to downtime, loss of availability, and potential operational disruptions, especially for public-facing services or internal applications supporting business-critical functions. Since Apache Tomcat is widely used across Europe in government, finance, healthcare, and other sectors, the risk of service interruption is significant. The vulnerability does not compromise data confidentiality or integrity directly but can indirectly affect business continuity and service reliability. Organizations relying on multipart upload functionality or handling large file uploads are particularly vulnerable. The ease of exploitation without authentication increases the threat landscape, making automated or mass scanning attacks feasible. This could lead to cascading effects if critical infrastructure or high-value targets are impacted, especially in countries with dense digital economies and extensive use of Java-based web applications.

European organizations should immediately assess their Apache Tomcat deployments to identify affected versions, including milestone and maintenance releases from 8.5.0 through 11.0.8. The primary mitigation is to upgrade to the fixed versions 11.0.9, 10.1.43, or 9.0.107 as soon as possible. Where immediate upgrades are not feasible, organizations should consider implementing network-level protections such as rate limiting and web application firewalls (WAFs) configured to detect and block abnormal multipart upload requests that could trigger the overflow. Monitoring upload sizes and patterns can help detect exploitation attempts. Additionally, disabling multipart upload functionality if not required can reduce attack surface. Security teams should also review logs for unusual upload activity and prepare incident response plans for potential DoS events. Regular vulnerability scanning and patch management processes should be enhanced to prevent similar issues. Finally, coordination with hosting providers and cloud services using Tomcat is recommended to ensure they have applied necessary patches.