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Symbol Tagging for dangerouslySetInnerHTML to Help Prevent XSS #10506

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sebmarkbage opened this Issue Aug 22, 2017 · 0 comments

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sebmarkbage commented Aug 22, 2017

If you're spreading props from a user provided source we have a XSS. E.g.

var data = JSON.parse(decodeURI(location.search.substr(1)));

function Foo(props) {
  return <div><div {...props} /><span>{props.content}</span></div>;
}

ReactDOM.render(<Foo {...data} />, container);

That's already true today because this URL is now an XSS hole:

?{"content":"Hello","dangerouslySetInnerHTML":{"__html":"<a%20onclick=\"alert(%27p0wned%27)\">Click%20me</a>"}}

This is very uncommon. There are many different ways to screw up getting user data. However doing that + also spreading is unusual. We decided in #3473 that React should add an extra layer of protection for these types of mistakes. This one is much more uncommon than the one in #3473 though.

You should already have a pretty centralized way of sanitizing these objects so it seems to me that adding a Symbol to this object shouldn't be that big of a deal though.

Either:

{ $$typeof:Symbol.for('react.rawhtml'), __html: myHTML }

or:

{ [Symbol.for('react.rawhtml')]: myHTML }
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