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CVE-2025-48866: Denial of Service Vulnerability in ModSecurity

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Overview

This report covers an important vulnerability, identified as CVE-2025-48866, that affects ModSecurity, an open-source, cross-platform web application firewall engine for Apache, IIS, and Nginx. The vulnerability can lead to a denial of service, potentially compromising systems or leading to data leaks. It is critical for organizations using ModSecurity to understand and address this vulnerability to protect their systems and data.

Vulnerability Summary

CVE ID: CVE-2025-48866
Severity: High (7.5 CVSS v3 Score)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Denial of Service and potential system compromise or data leakage

Affected Products

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Product | Affected Versions

ModSecurity for Apache | < 2.9.10 ModSecurity for IIS | < 2.9.10 ModSecurity for Nginx | < 2.9.10 How the Exploit Works

The vulnerability exists within the `sanitiseArg` alias `sanitizeArg` actions of ModSecurity. An attacker can submit a large number of arguments in an HTTP request, which ModSecurity fails to handle properly. This results in a denial of service due to resource exhaustion. The same flaw can potentially be leveraged to compromise the system or leak data.

Conceptual Example Code

Here’s a conceptual example of a HTTP request that exploits the vulnerability:

POST /vulnerable/endpoint HTTP/1.1
Host: target.example.com
Content-Type: application/x-www-form-urlencoded
arg1=value&arg2=value&arg3=value&arg4=value&...&argN=value

In the above example, ‘argN’ represents an excessive number of arguments that exploit the vulnerability.

Mitigation Guidance

The recommended mitigation is to upgrade to ModSecurity version 2.9.10 or later, which has a fix for this specific vulnerability. If upgrading is not immediately possible, a temporary workaround is to avoid using rules that contain the `sanitiseArg` or `sanitizeArg` action. Utilizing a web application firewall (WAF) or intrusion detection system (IDS) can also provide temporary mitigation.

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Disclaimer:

The information and code presented in this article are provided for educational and defensive cybersecurity purposes only. Any conceptual or pseudocode examples are simplified representations intended to raise awareness and promote secure development and system configuration practices.

Do not use this information to attempt unauthorized access or exploit vulnerabilities on systems that you do not own or have explicit permission to test.

Ameeba and its authors do not endorse or condone malicious behavior and are not responsible for misuse of the content. Always follow ethical hacking guidelines, responsible disclosure practices, and local laws.

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