Risks of Allowing User-Generated HTML
User-generated HTML can make applications interactive and engaging, but it also poses serious security and usability risks if not handled carefully. Attackers can exploit this by injecting harmful markup or scripts.
Cross-Site Scripting (XSS): Attackers may insert
<script>tags, event handlers (likeonclick), or malicious inline JavaScript to steal cookies or perform unauthorized actions.Phishing and Tabnabbing: Malicious
<a>tags withtarget="_blank"can be used for reverse tabnabbing attacks, tricking users into entering sensitive information.CSS Injection: Inline styles or
<style>blocks could manipulate the page’s look, hide warnings, or overlay fake UI elements.Form Hijacking: Injected
<form>elements may capture user credentials and send them to an attacker’s server.Denial of Service (DoS): Attackers could inject very large HTML or recursive elements (like nested
<iframe>) to crash the page or slow performance.
In short: Allowing raw user-generated HTML without sanitization is dangerous. Always sanitize and validate user input on both client and server sides, and consider using libraries that strip unsafe tags and attributes.