What should a website operator do to prevent XSS attacks?
To ensure that your web application isn’t vulnerable to XSS attacks, you must view all received input values as being unsafe. Before they are received by the web server they should be verified appropriately. The most secure method is to create a whitelist, just like the NoScript extension for clients. As long as the capacity allows it, you should scan the inputs on your website and only trusted content should be allowed. This way you create excellent protection against cross-site scripting.
In addition to the input data, the data output should also be protected. For this reason, it’s necessary for the HTML metacharacters to be replaced by appropriate character references. As a result, the metadata is classified as normal characters and potentially infiltrated scripts cannot start. Most programming and scripting languages such as Perl, JavaScript, or PHP already possess predefined features for character replacement or masking, which they can promptly use. Furthermore, you can fend off simple XSS attacks by using a web application firewall.
Cross-site scripting often set the gears in motion for more serious attacks. You can thwart their attempts with extensive protection of your web server’s inward and outward data streams.