The impact of authentication vulnerabilities can be severe. If an attacker bypasses authentication or brute-forces their way into another user's account, they have access to all the data and functionality that the compromised account has. If they are able to compromise a high-privileged account, such as a system administrator, they could take full control over the entire application and potentially gain access to internal infrastructure.
Even compromising a low-privileged account might still grant an attacker access to data that they otherwise shouldn't have, such as commercially sensitive business information. Even if the account does not have access to any sensitive data, it might still allow the attacker to access additional pages, which provide a further attack surface. Often, high-severity attacks are not possible from publicly accessible pages, but they may be possible from an internal page.
