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CVE-2025-47947: Denial of Service Vulnerability in ModSecurity Web Application Firewall

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Overview

The CVE-2025-47947 vulnerability is a significant security flaw discovered in ModSecurity, an open-source web application firewall widely used across platforms such as Apache, IIS and Nginx. This vulnerability is critical due to its potential to cause a denial of service attack, potentially leading to system compromise or data leakage.

Vulnerability Summary

CVE ID: CVE-2025-47947
Severity: High (CVSS: 7.5)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Denial of service, potential system compromise or data leakage

Affected Products

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Product | Affected Versions

ModSecurity for Apache | Up to and including 2.9.8
ModSecurity for IIS | Up to and including 2.9.8
ModSecurity for Nginx | Up to and including 2.9.8

How the Exploit Works

The vulnerability lies in the `sanitiseMatchedBytes` action in ModSecurity. When the payload’s content type is `application/json`, and a rule which executes a `sanitiseMatchedBytes` action is triggered, the application becomes susceptible to a denial of service attack. The attacker can leverage this vulnerability to cause the system to consume excessive resources, leading to a denial of service.

Conceptual Example Code

Here is a conceptual example of how an attacker might exploit this vulnerability:

POST /vulnerable/endpoint HTTP/1.1
Host: target.example.com
Content-Type: application/json
{
"sanitiseMatchedBytes": "This is a malicious payload that triggers a denial of service attack..."
}

The above request, when processed by a vulnerable version of ModSecurity, could lead to a denial of service attack.

Mitigation

The most effective mitigation for this vulnerability is to apply the vendor-supplied patch, which is available at pull request 3389 and is expected to be included in version 2.9.9. In situations where immediate patching is not possible, deploying a web application firewall or intrusion detection system as a temporary mitigation measure is recommended. However, it is crucial to note that these are only stop-gap measures and the patch should be applied as soon as possible to fully mitigate the vulnerability.

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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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