Hey everyone,
I’ve been wondering how website builders like Webflow, SquareSpace, or even platforms like CodePen allow you to add custom HTML, CSS, and JavaScript (e.g., custom <head> code). How do they take that input, store it, and render it on the live site?
I know there’s probably some protection since most clients wouldn’t want to sabotage their own site with malicious code, but I’m sure some pentester has tried to break it (maybe even drop a SquareSpace table? 
).
So how do these builders handle it securely? Is it all about client-side filtering (like Twig or something)? Or is there some magic going on with SQL?
Any insights would be awesome. Thanks!
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They probably sanitize the code before storing it, making sure no harmful scripts can run. Things like SQL injections would be hard to pull off unless someone messed up real bad on the backend. As for client-side filtering, I think Twig is more for templating, not security, but some builders might use a similar system for filtering dangerous stuff.
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It’s a mix of things, really. Some builders use something called Content Security Policy (CSP), which limits what the user’s custom code can do, even if it has vulnerabilities. So, for example, your custom JavaScript can’t make unauthorized requests. Plus, they have filters for things like XSS (cross-site scripting) before code gets stored.
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Good question! In addition to sanitizing inputs, a lot of these platforms likely have a built-in “sandbox” environment for running custom code. That way, even if someone manages to sneak in something dangerous, it’s executed in a controlled space where it can’t do harm. I’d imagine their devs are always patching stuff too.
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Yeah, SQL injection wouldn’t really apply here unless they’re doing something super weird with their database structure. It’s more about cross-site scripting and how they clean the input before it’s processed. Like, they probably strip out harmful tags or attributes, but they still allow the custom stuff to work. Makes me wonder if any builder has ever had a major breach because of this. 
I bet they use something server-side to filter the code, but I’m sure they also rely on browser-based solutions like CSP. Also, some of these builders might be monitoring for unusual activity constantly, so if something sketchy happens, they can shut it down fast. Wouldn’t be surprised if they had an internal blacklist of common attack patterns.