CVE-2025-52520: Apache Tomcat Integer Overflow DoS Flaw

CVE-2025-52520 Overview

For some unlikely configurations of multipart upload, an Integer Overflow vulnerability in Apache Tomcat could lead to a DoS via bypassing of size limits. This vulnerability affects multiple versions of Apache Tomcat, specifically: 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.

Critical Impact

This vulnerability could allow malicious actors to perform a denial of service attack by exploiting an integer overflow in multipart upload configurations.

Affected Products

• Apache Tomcat 11.0.0-M1 to 11.0.8
• Apache Tomcat 10.1.0-M1 to 10.1.42
• Apache Tomcat 9.0.0.M1 to 9.0.106

Discovery Timeline

• Not Available - Vulnerability discovered by Not Available
• Not Available - Responsible disclosure to Apache
• Not Available - CVE CVE-2025-52520 assigned
• Not Available - Apache releases security patch
• 2025-07-10 - CVE CVE-2025-52520 published to NVD
• 2025-11-04 - Last updated in NVD database

Technical Details for CVE-2025-52520

Vulnerability Analysis

The vulnerability arises from an integer overflow in the handling of multipart uploads. Specifically, the issue occurs when size limits are bypassed due to improper calculations, leading to a potential denial of service (DoS).

Root Cause

The integer overflow results from improper validation of multipart upload data size, causing calculations to exceed expected boundaries.

Attack Vector

This vulnerability can be exploited remotely over a network through specially crafted HTTP requests utilizing multipart uploads.

// Example exploitation code (sanitized)
InputStream inputStream = ...; 
byte[] buffer = new byte[1024];
while ((bytesRead = inputStream.read(buffer)) != -1) {
    // Process upload
}

Detection Methods for CVE-2025-52520

Indicators of Compromise

• Unusual spikes in resource utilization
• Log entries indicating abnormal upload activity
• Unexpected server downtime or crash logs

Detection Strategies

Implement continuous monitoring of server logs for unexpected HTTP request patterns related to multipart uploads. Consider using anomaly detection mechanisms to identify potential exploit attempts.

Monitoring Recommendations

Utilize monitoring tools to track server load and alert on significant deviations from normal operational patterns. Assess network traffic for unusually large or malformed multipart requests.

How to Mitigate CVE-2025-52520

Immediate Actions Required

• Update Apache Tomcat to versions 11.0.9, 10.1.43, or 9.0.107
• Implement input validation to enforce strict size limits on uploads
• Monitor traffic for anomalies and perform regular security assessments

Patch Information

Users are advised to upgrade Apache Tomcat to versions that contain the fixes: 11.0.9, 10.1.43, or 9.0.107, as specified in the Apache advisory.

Workarounds

Limit the maximum size of multipart uploads in the configuration while applying network-level restrictions on upload traffic.

# Configuration example
<Connector port="8080" maxPostSize="2097152" maxSavePostSize="4096"/>