Validating form input javascript

19 Jan

For more information on XSS filter evasion please see the XSS Filter Evasion Cheat Sheet.$"); public void do Post( Http Servlet Request request, Http Servlet Response response) Be aware that any Java Script input validation performed on the client can be bypassed by an attacker that disables Java Script or uses a Web Proxy.Ensure that any input validation performed on the client is also performed on the server.It is very difficult to validate rich content submitted by a user.For more information, please see the cheatsheet on Sanitizing HTML Markup with a Library Designed for the Job.

To normalise an email address input, you would convert the domain part ONLY to lowercase.

Unfortunately this does and will make input harder to normalise and correctly match to a users intent.

SSN, date, currency symbol) while semantic validation should enforce correctness of their values in the specific business context (e.g.

start date is before end date, price is within expected range).

It's also free-form text input that highlights the importance of proper context-aware output encoding and quite clearly demonstrates that input validation is not the primary safeguards against Cross-Site Scripting — if your users want to type apostrophe (') or less-than sign ( References: Input validation of free-form Unicode text in Python Developing regular expressions can be complicated, and is well beyond the scope of this cheat sheet.

There are lots of resources on the internet about how to write regular expressions, including: and the OWASP Validation Regex Repository.

It is always recommended to prevent attacks as early as possible in the processing of the user’s (attacker's) request.