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.
