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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.
Input validation can be implemented using any programming technique that allows effective enforcement of syntactic and semantic correctness, for example: , where the ' character is fully legitimate.
For more information, please see the cheatsheet on Sanitizing HTML Markup with a Library Designed for the Job.Detailed information on XSS prevention here: OWASP XSS Prevention Cheat Sheet Many websites allow users to upload files, such as a profile picture or more. Many web applications do not treat email addresses correctly due to common misconceptions about what constitutes a valid address.Specifically, it is completely valid to have an mailbox address which: At the time of writing, RFC 5321 is the current standard defining SMTP and what constitutes a valid mailbox address.It is always recommended to prevent attacks as early as possible in the processing of the user’s (attacker's) request.Input validation can be used to detect unauthorized input before it is processed by the application.
In summary, input validation should: Example validating the parameter “zip” using a regular expression.