Cross Site Scripting, OR XSS, is a way for hackers to gather your website’s user data by using malicious markup or JavaScript code to trick a user, or their browser, to follow a bad link or present their login details to a fake login screen that instead of logging them in, steals their personal information. The best way to defend against XSS is following...
Strip html tags like h1, <script>, for this use php strip_tags function
escape the data before showing on website, for this use htmlentities function.
An Example:
A basic example of XSS is when a malicious user injects a script in a legitimate shopping site URL which in turn redirects a user to a fake but identical page. The malicious page would run a script to capture the cookie of the user browsing the shopping site, and that cookie gets sent to the malicious user who can now hijack the legitimate user’s session. Although no real hack has been performed against the shopping site, XSS has still exploited a scripting weakness in the page to snare a user and take command of his session. A trick which often is used to make malicious URLs less obvious is to have the XSS part of the URL encoded in HEX (or other encoding methods). This will look harmless to the user who recognizes the URL he is familiar with, and simply disregards and following ‘tricked’ code which would be encoded and therefore inconspicuous.
