Understanding Broken Access Control Vulnerabilities and How to Bypass 403 Endpoints

Broken access control vulnerabilities can pose a significant threat to a web application's security. Such vulnerabilities allow unauthorized users to access restricted resources, circumventing the standard security procedures. By exploiting these vulnerabilities, attackers can gain access to sensitive information or systems, resulting in data breaches or other serious security incidents.

One of the common ways to prevent unauthorized access is by returning a 403 forbidden response for sensitive endpoints such as .htaccess or config.php. The HTTP 403 Forbidden response status code indicates that the server understands the request but refuses to authorize it. However, if the access control mechanism applied is weak, attackers can bypass the security controls and gain access to restricted resources.

In a recent discovery of an IoT service delivery platform, the researcher used directory enumeration with dirbuster wordlists and found a /console endpoint that returned a 403 response. The /console endpoint served as a lead, and the researcher tried bypassing the 403 endpoint using various techniques.

One of the techniques used was path fuzzing, which involves altering the URL path to bypass the access control check. The researcher tried using . or %2e in the URL path (/%2e/console), which allowed them to bypass the access control check and gain access to the internal system console manager.

To automate the bypass techniques, the researcher used the 403 Bypasser Burp extension by Gil Nothmann, which quickly provided the necessary results. They also added rules in Burp to prepend every necessary request with /%2e/ to conveniently browse through the console manager.

The console manager provided sensitive component data, including build details, OS details, and user details, and also offered a CLI component for code execution.

In conclusion, broken access control vulnerabilities can be dangerous and should be addressed promptly. Proper access control mechanisms must be implemented to prevent unauthorized access to sensitive resources. Path fuzzing can be a useful technique to bypass 403 endpoints, but it is essential to ensure that it is not used for malicious purposes. It is also advisable to use tools like the 403 Bypasser Burp extension to automate bypass techniques and avoid manual errors.