CVE-2019-11391 Explained : Impact and Mitigation

A vulnerability has been identified in the OWASP ModSecurity Core Rule Set (CRS) version 3.1.0 that allows remote attackers to trigger a denial of service (ReDOS) by inputting a specifically crafted string. The issue is disputed by the software maintainer.

Understanding CVE-2019-11391

This CVE involves a vulnerability in the OWASP ModSecurity Core Rule Set (CRS) version 3.1.0 that could lead to a denial of service (ReDOS) attack.

What is CVE-2019-11391?

The vulnerability in the configuration file of the CRS allows remote attackers to exploit a flaw and cause a denial of service by inputting a specially crafted string.

The Impact of CVE-2019-11391

The vulnerability enables remote attackers to trigger a denial of service (ReDOS) attack, potentially disrupting the availability of the affected system.

Technical Details of CVE-2019-11391

This section provides more technical insights into the CVE.

Vulnerability Description

The flaw in the /rules/REQUEST-933-APPLICATION-ATTACK-PHP.conf file allows attackers to exploit nested repetition operators, leading to a denial of service (ReDOS) attack.

Affected Systems and Versions

OWASP ModSecurity Core Rule Set (CRS) version 3.1.0

Exploitation Mechanism

Attackers can exploit the vulnerability by inputting a crafted string starting with $a# and containing nested repetition operators.

Mitigation and Prevention

To address CVE-2019-11391, follow these mitigation strategies:

Immediate Steps to Take

Monitor and restrict input data to prevent specially crafted strings.
Regularly update ModSecurity and the Core Rule Set to the latest versions.

Long-Term Security Practices

Implement input validation mechanisms to filter out malicious input.
Conduct regular security assessments and audits to identify vulnerabilities.

Patching and Updates

Apply patches and updates provided by OWASP ModSecurity to fix the vulnerability.