First, ensure that Burp is correctly configured with your browser.
With Burp Proxy "Intercept" turned off, visit the web application you are testing in your browser.
Go to the Scanner "Options" tab and locate the "Static Code Analysis" options.
By default, Burp only performs static analysis for bugs like XSS during active scanning, but you can also enable this for passive scanning.
Now, visit the page of the website you wish to test for XSS vulnerabilities.
Burp Scanner will now passively detect any DOM XSS vulnerabilities as you browse.
Go to the Scanner "Results" tab to view any potential vulnerabilities.
The Scanner "Advisory" tab provides further information on the issue.
In this example, the unfiltered input from a URL in to an eval() statement is worth further investigation.
In the "Response 2" tab you can see how a value is read from a "document.url" file and written to "eval()".
The information in these tabs provides details of what will be needed when attempting to produce a valid payload for a proof of concept.
In this example we can discern that the parameter name must be equal to the param variable when the function is called. This satisfies the "if" statement.
The function called is "trigMMlurl".
We can then discern that the parameter name is "menu".
We can also use single quotation marks to break out of the function.
The payload is added to the URL in the address bar of your browser.
The payload we have used to produce the proof of concept is ?menu='-alert(1)-'.