XSS Embedded IFrames

Today we saw a variety of pages being advertised that have search.htm and other pages vulnerable to cross-site scripting (XSS) being used to inject an iframe to a malicious webpage redirector. To an unknowing user following such an advertisement, they would believe that they were just visiting the intended host site unaware that the iframe was also redirecting them to malicious content.

Here are a few examples with some of the malicious XSS advertisements (do not follow these or other "hxxp" URLs below):


In each of the above examples, the parameter passed to the server's .htm or .php file is a string that includes encoded HTML. When the server processes the parameter, it displays the original parameter (users usually want to see their query string) and its results. Because the original parameter is displayed on the page without any sanitization for this type of encoded HTML, it is possible for this XSS to take place. The encoded HTML in each case is hexadecimal encoded HTML:

%3C%2F%74%69%74%6C%65%3E%3C%69%66%72%61%6D%65%20%73%72%63%3D%2F%2F%61%73%6B%35%2E%65%75%3E

which decodes to a closing tag for the query string, followed by the malicious iframe to embed: