Nessus provides some of the first steps to web application testing, such as identifying the web server software and technologies, detecting vulnerabilities in common/popular web application software and rudimentary CGI application testing. Nessus can help with both of these tasks, and provide valuable information that will help with your testing. The second form of testing is when you are given the URL, and typically credentials, to the web application and asked to test it specifically. You need to first find and enumerate which web applications are running and then run targeted scans that specifically look for web vulnerabilities. The web applications running within this space will usually be tested generically, but they may not specifically test for web vulnerabilities in a general scan. The first is part of a larger so-called 'blind' test, where you are given a range of IP addresses and asked to test the devices and systems within those ranges. There are two different approaches when performing web application testing.

You can read more about this topic in The Nessus Port Scanning Engine: An Inside Look, and Web Application Scanning with Nessus.

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