A vulnerability scanner is a computer program designed to assess computers, computer systems, networks or applications for known weaknesses. In plain words, these scanners are used to discover the weak points or poorly constructed parts. It's utilized for the identification and detection of vulnerabilities relating to mis-configured assets or flawed software that resides on a network-based asset such as a firewall, router, web server, application server, etc. Modern vulnerability scanners will allow for both authenticated and unauthenticated scans to occur.
Authenticated Scans allow for the scanner to directly access network based assets using remote administrative protocols such as secure shell (SSH) or remote desktop protocol (RDP) and authenticate using provided system credentials. This allows the vulnerability scanner to access low-level data, such as specific services and configuration details of the host operating system. It’s then able to provide detailed and accurate information about the operating system and installed software, including configuration issues and missing security patches.
Unauthenticated Scans is a method that can result in a high number of false positives and is unable to provide detailed information about the assets operating system and installed software. This method is typically used by threat actors or security analyst trying determine the security posture of externally accessible assets