CVE-2025-52520 is an integer overflow vulnerability classified under CWE-190 that affects the multipart upload functionality in Apache Tomcat versions 8.5.0 through 8.5.100 (EOL), 9.0.0.M1 through 9.0.106, 10.1.0-M1 through 10.1.42, and 11.0.0-M1 through 11.0.8. The vulnerability occurs when certain multipart upload configurations cause size limits to be bypassed due to an integer overflow or wraparound condition. This overflow can lead to denial of service (DoS) by allowing an attacker to submit specially crafted multipart requests that exceed intended size constraints without being properly checked. The flaw does not require any authentication or user interaction, making it remotely exploitable over the network. The vulnerability impacts availability but does not affect confidentiality or integrity directly. Apache has addressed this issue in versions 11.0.9, 10.1.43, and 9.0.107 by correcting the integer handling logic in multipart upload processing. No known exploits have been reported in the wild as of the publication date, but the vulnerability’s nature and ease of exploitation warrant immediate attention. The issue is particularly relevant for organizations using Tomcat as a web server or servlet container, as multipart uploads are common in web applications handling file uploads. The vulnerability’s presence in multiple major Tomcat branches, including some EOL versions still in use, increases the scope of affected systems globally.

For European organizations, the primary impact of CVE-2025-52520 is the potential for denial of service attacks that can disrupt web services and applications hosted on Apache Tomcat servers. This can lead to operational downtime, loss of availability of critical business applications, and potential reputational damage. Industries that rely heavily on web-based services, such as finance, healthcare, government, and e-commerce, could experience significant service interruptions. Since the vulnerability does not compromise confidentiality or integrity, data breaches are not a direct concern; however, service outages can indirectly affect business continuity and customer trust. The ease of remote exploitation without authentication increases the risk of automated attacks or exploitation by opportunistic threat actors. European organizations with large-scale deployments of Tomcat, especially those using older or EOL versions, face heightened risk. Additionally, regulatory requirements such as GDPR emphasize service availability and incident response, making timely patching critical to compliance and risk management.

1. Immediate upgrade to Apache Tomcat versions 11.0.9, 10.1.43, or 9.0.107, which contain the fix for this vulnerability. Avoid using EOL versions as they no longer receive security updates. 2. Review and harden multipart upload configurations to enforce strict size limits and validate input parameters, reducing the attack surface. 3. Implement network-level protections such as web application firewalls (WAFs) to detect and block suspicious multipart upload requests that may attempt to exploit this overflow. 4. Monitor Tomcat server logs for unusual multipart upload activity or repeated requests that could indicate exploitation attempts. 5. Conduct regular vulnerability scanning and penetration testing focused on multipart upload functionality to identify potential misconfigurations or residual risks. 6. Employ rate limiting and connection throttling on endpoints handling file uploads to mitigate potential DoS attempts. 7. Maintain an inventory of all Tomcat instances across the organization, including development and testing environments, to ensure comprehensive patch management. 8. Educate development and operations teams about secure handling of multipart requests and the importance of timely patching.