Unable to pass '<' in URL as parameter

Why am I unable to pass '<' character as a parameter in the URL? If I do:

http://localhost:9566/?myVar=2 that is ok

But I cannot do:

http://localhost:9566/?myVar=<foo> Why does this give me an error?

When I URL-encode <foo> I get %3Cfoo%3E.

And when I do http://localhost:9566/?myVar=%3Cfoo%3E, I still get the same error:

This is by design. The characters you are trying to pass could potentially be used in a Cross Site Scripting (XSS) attack.

Here are a few links to get you started on understanding what XSS is:

• https://www.owasp.org/index.php/Cross-site_Scripting_%28XSS%29
• http://www.cgisecurity.com/xss-faq.html

While you can disable this type of validation I would not recommend it. Do you really need to pass a tag in a query string parameter?