When you configure a scan or policy's Credentials, the Nessus scanner can be granted local access to scan the target system without requiring an agent. This can facilitate scanning of a very large network to determine local exposures or compliance violations. As noted, some steps of policy creation may be optional. Once created, the policy is saved with recommended settings.

Nessus leverages the ability to log into remote Linux hosts via Secure Shell (SSH); and with Windows hosts, Nessus leverages a variety of Microsoft authentication technologies. Note that Nessus also uses the Simple Network Management Protocol (SNMP) to make version and information queries to routers and switches.

The scan or policy’s Credentials page allows you to configure the Nessus scanner to use authentication credentials during scanning. Configuring credentials allows Nessus to perform a wider variety of checks that result in more accurate scan results.

There are several forms of authentication supported including but not limited to databases, SSH, Windows, network devices, patch management servers, and various plaintext authentication protocols.

In addition to operating system credentials, Nessus supports other forms of local authentication.

The following types of credentials are managed in the Credentials section of the scan or policy:

Credentialed scans can perform any operation that a local user can perform. The level of scanning is dependent on the privileges granted to the user account. The more privileges the scanner has via the login account (e.g., root or administrator access), the more thorough the scan results.

Note: Nessus opens several concurrent authenticated connections. Ensure that the host being audited does not have a strict account lockout policy based on concurrent sessions.

If a scan contains multiple instances of one type of credential, Nessus tries the credentials on each scan target in the order you added the credentials to the scan.

Note: Nessus uses the first credential that allows successful login to perform credentialed checks on the target. After a credential allows a successful login, Nessus does not try any of the other credentials in the list, even if a different credential has greater privileges.