Originally published on the Bug Circuit blog.
Cross-site scripting (XSS) is a security bug that lets an attacker sneak their own code into a page your visitors trust, so it runs inside their browser as if your site wrote it — quietly stealing login sessions, redirecting payments, or planting fake forms. It's one of the oldest and still most common web vulnerabilities, and it doesn't require breaking into your server — just finding one spot on your site that echoes back user input without cleaning it up first.
This is for owners of WordPress sites, Shopify stores, indie SaaS apps, or small business sites who've heard the term "XSS," maybe seen it flagged by a scanner, and want to know in plain English what it actually does and whether their contact or comment form is a target. By the end, you'll know how to test for it yourself and what a real fix looks like.
The short version: how XSS actually works
Every web page is a mix of your content and, sometimes, content your visitors typed in — a comment, a search term, a name field, a support ticket. Your site's job is to display that input back safely, as plain text.
