A recently discovered vulnerability (CVE-2025-31651) in Apache Tomcat exposes a risk of improper neutralization of escape, meta, or control sequences. This flaw allows specially crafted requests to bypass specific rewrite rules, thereby potentially compromising the enforced security constraints within your system. The severity of this vulnerability is proportional to the extent of your rewrite rule configuration's capabilities.

Affected Apache Tomcat versions include 11..-M1 through 11..5, 10.1.-M1 through 10.1.39, and 9...M1 through 9..102. To mitigate this risk, users should upgrade to the fixed version.

Details

Original references: Link 1 | Link 2 | Link 3

In certain cases, your rewrite rule configurations may not perform effective neutralization of escape, meta, or control sequences. This vulnerability, identified as CVE-2025-31651, allows cyber attackers to send specially crafted requests that can bypass some rewrite rules, leading to a bypass of enforced security constraints in your system.

Here's a code snippet that represents a rewrite rule that could be bypassed using a malformed request:

RewriteRule ^([a-zA-Z-9]+)$ index.php?page=$1 [L]

The issue arises when an attacker crafts a request such as /page<script>alert(1)<%2Fscript> that bypasses the above rewrite rule, which should enforce a security constraint that only allows alpha-numeric characters in the URL.

To demonstrate this exploit, consider the following request

https://yourdomain.com/page<script>alert(1)<%2Fscript>;

The server would receive the request and, due to the vulnerability, the request would bypass the rewrite rule leading to the potential execution of malicious scripts within your system.

Mitigation

To address this vulnerability, users should upgrade their Apache Tomcat installations. The specific fixed versions are available at the following links:

- Apache Tomcat 11: Fixed Version 11..6
- Apache Tomcat 10.1: Fixed Version 10.1.40
- Apache Tomcat 9: Fixed Version 9..103

Additionally, you may also consider implementing server-side input validation and sanitization to further protect your system from possible exploits that bypass rewrite rules. This may also involve the review and adjustment of your existing rewrite rule configurations.

Conclusion

This vulnerability, CVE-2025-31651, is an important issue to address as it can lead to a compromise of the enforced security constraints within your Apache Tomcat installations. Users should upgrade their installations to the new fixed version to ensure that their systems are protected from potential exploits. Furthermore, implementing thorough server-side input validation and sanitization is an essential step in securing your system against compromised rewrite rules.

Timeline

Published on: 04/28/2025 20:15:20 UTC
Last modified on: 05/05/2025 20:14:47 UTC