CVE-2025-52520 is an Integer Overflow vulnerability classified under CWE-190 that affects multiple versions of the Apache Tomcat server, specifically 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, as well as older EOL versions such as 8.5.0 through 8.5.100. The vulnerability arises in the multipart upload handling component of Apache Tomcat, where certain unlikely configurations can trigger an integer overflow or wraparound condition. This overflow can cause the server to bypass configured size limits on multipart uploads, potentially allowing an attacker to send excessively large payloads. The primary consequence of this vulnerability is a Denial of Service (DoS) condition, where the server may become unresponsive or crash due to resource exhaustion or improper handling of the oversized request. The vulnerability does not impact confidentiality or integrity directly, as it does not allow code execution or data leakage, but it severely affects availability. The CVSS v3.1 base score is 7.5 (High), reflecting the 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 confidentiality or integrity impact (C:N/I:N), and high availability impact (A:H). No known exploits are reported in the wild at the time of publication. The Apache Software Foundation has addressed this issue in versions 11.0.9, 10.1.43, and 9.0.107, and users are strongly advised to upgrade to these fixed versions to mitigate the risk. This vulnerability is particularly relevant for environments that accept multipart uploads, such as web applications handling file uploads, where attackers could exploit the integer overflow to disrupt service availability.

For European organizations, the impact of CVE-2025-52520 can be significant, especially for those relying on Apache Tomcat as a core component of their web infrastructure. Many enterprises, government agencies, and service providers in Europe use Tomcat to host web applications, APIs, and services that handle file uploads. Exploitation of this vulnerability could lead to service outages, disrupting business operations, customer access, and critical online services. This is particularly critical for sectors such as finance, healthcare, public administration, and e-commerce, where availability is paramount. A successful DoS attack could also lead to reputational damage and potential regulatory scrutiny under frameworks like GDPR if service disruptions affect user data processing. Additionally, the vulnerability could be leveraged as part of a multi-stage attack to distract or exhaust resources while other attacks are conducted. Given the low complexity and lack of required privileges or user interaction, attackers could automate exploitation attempts, increasing the risk of widespread impact.

To mitigate CVE-2025-52520, European organizations should: 1) Immediately upgrade Apache Tomcat installations to the fixed versions 11.0.9, 10.1.43, or 9.0.107 depending on their current major version. 2) Review and tighten multipart upload configurations to enforce strict size limits and validate input parameters to prevent malformed requests that could trigger integer overflows. 3) Implement web application firewalls (WAFs) with rules to detect and block suspicious multipart upload patterns that exceed expected sizes or exhibit anomalous behavior. 4) Monitor server logs and network traffic for unusual spikes in multipart upload requests or errors indicative of overflow attempts. 5) For legacy systems that cannot be immediately upgraded, consider isolating Tomcat servers behind reverse proxies that can enforce upload size limits and rate limiting. 6) Conduct penetration testing and vulnerability scanning focused on multipart upload handling to verify the effectiveness of mitigations. 7) Maintain an incident response plan to quickly address potential DoS events and ensure business continuity. These steps go beyond generic patching advice by emphasizing configuration hardening, monitoring, and layered defenses tailored to the multipart upload vector.