CVE-2025-52520 is a high-severity integer overflow vulnerability identified in the Apache Software Foundation's Apache Tomcat server, affecting versions from 11.0.0-M1 through 11.0.8, 10.1.0-M1 through 10.1.42, and 9.0.0.M1 through 9.0.106. The vulnerability arises specifically in the handling of multipart uploads under certain unlikely configurations. An integer overflow or wraparound (CWE-190) occurs when the size calculations for multipart upload data exceed the maximum value an integer can hold, causing the size limit checks to be bypassed. This bypass can lead to a denial of service (DoS) condition, as the server may accept and attempt to process data beyond intended limits, potentially exhausting resources or causing crashes. The vulnerability does not impact confidentiality or integrity directly but affects availability by enabling attackers to disrupt service. The CVSS v3.1 base score is 7.5, reflecting a high severity with network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), no impact on confidentiality or integrity (C:N/I:N), and high impact on availability (A:H). No known exploits are currently reported in the wild. The recommended remediation is to upgrade Apache Tomcat to versions 11.0.9, 10.1.43, or 9.0.107, which contain fixes for this issue.

For European organizations, this vulnerability poses a significant risk to the availability of web applications and services relying on Apache Tomcat servers, which are widely used across industries including finance, government, healthcare, and e-commerce. A successful exploitation could lead to denial of service, causing downtime, service disruption, and potential loss of business continuity. This is particularly critical for organizations with high availability requirements or those providing essential services. Since no authentication or user interaction is required, attackers can remotely trigger the vulnerability, increasing the risk of automated or large-scale attacks. The bypass of multipart upload size limits could also lead to resource exhaustion, impacting server performance and potentially cascading to affect other dependent systems. Although no data breach or integrity compromise is indicated, the operational impact and reputational damage from service outages can be substantial.

European organizations should prioritize upgrading Apache Tomcat to the fixed versions (11.0.9, 10.1.43, or 9.0.107) as the primary mitigation step. Until upgrades are applied, organizations can implement strict network-level controls to limit exposure of Tomcat servers to untrusted networks, including firewall rules and web application firewalls (WAF) configured to detect and block abnormal multipart upload requests. Monitoring and alerting on unusual multipart upload traffic patterns can help detect exploitation attempts. Additionally, organizations should review and tighten multipart upload configurations to avoid unlikely or non-standard settings that could trigger the vulnerability. Regular vulnerability scanning and patch management processes should be enforced to ensure timely detection and remediation of such issues. Finally, incident response plans should be updated to include scenarios involving DoS attacks targeting multipart upload functionality.