Textarea not validating
Data from all potentially untrusted sources should be subject to input validation, including not only Internet-facing web clients but also backend feeds over extranets, from suppliers, partners, vendors or regulators, each of which may be compromised on their own and start sending malformed data.Input Validation should not be used as the primary method of preventing XSS, SQL Injection and other attacks which are covered in respective cheat sheets but can significantly contribute to reducing their impact if implemented properly.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).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.If the input field comes from a fixed set of options, like a drop down list or radio buttons, then the input needs to match exactly one of the values offered to the user in the first place.Free-form text, especially with Unicode characters, is perceived as difficult to validate due to a relatively large space of characters that need to be whitelisted.
For more information, please see the cheatsheet on Sanitizing HTML Markup with a Library Designed for the Job.
Input validation is performed to ensure only properly formed data is entering the workflow in an information system, preventing malformed data from persisting in the database and triggering malfunction of various downstream components.
Input validation should happen as early as possible in the data flow, preferably as soon as the data is received from the external party.
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.