Configuration Management / User Agent-Dependent Response
User agent-dependent response is a type of configuration management vulnerability (CWE-16) that can occur in web and API applications. It occurs when a web application or API server responds differently to requests based on the user agent string sent by the client. This can lead to information disclosure, or allow access to functions that should not be accessible for that user agent. According to the OWASP Testing Guide, this vulnerability can be caused by the application incorrectly parsing user-agent strings, or by failing to filter out malicious user-agent strings.
This vulnerability can lead to serious security issues, such as information disclosure and unauthorized access to sensitive data. If an attacker can identify and craft a malicious user-agent string, they can gain access to data or functions that should be restricted. As such, this vulnerability can result in a major security breach and should be addressed as soon as possible.
The solution to this vulnerability is to validate user-agent strings on the server side before allowing a user access to the system. This can be done by creating a whitelist of valid user-agent strings, and rejecting any strings that are not on the whitelist. Additionally, any user-agent strings that contain malicious characters should be blocked.