ReactJS is quite safe by design since
- String variables in views are escaped automatically
- With JSX you pass a function as the event handler, rather than a string that can contain malicious code
so a typical attack like this will not work
const username = "<img onerror="alert(\"Hacked!\")" src="https://stackoverflow.com/questions/33644499/invalid-image" />";
class UserProfilePage extends React.Component {
render() {
return (
<h1> Hello {username}!</h1>
);
}
}
ReactDOM.render(<UserProfilePage />, document.querySelector("#app"));<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="app"></div>but …
❗❗❗Warning❗❗❗
There are still some XSS attack vectors that you need to handle yourself in React!
1. XSS via dangerouslySetInnerHTML
When you use dangerouslySetInnerHTML you need to make sure the content doesn’t contain any javascript. React can’t do here anything for you.
const aboutUserText = "<img onerror="alert(\"Hacked!\");" src="https://stackoverflow.com/questions/33644499/invalid-image" />";
class AboutUserComponent extends React.Component {
render() {
return (
<div dangerouslySetInnerHTML={{"__html": aboutUserText}} />
);
}
}
ReactDOM.render(<AboutUserComponent />, document.querySelector("#app"))<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="app"></div>2. XSS via a.href attribute
Example 1: Using javascript:code
Click on “Run code snippet” -> “My Website” to see the result
const userWebsite = "javascript:alert('Hacked!');";
class UserProfilePage extends React.Component {
render() {
return (
<a href={userWebsite}>My Website</a>
)
}
}
ReactDOM.render(<UserProfilePage />, document.querySelector("#app"));<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="app"></div>Example 2: Using base64 encoded data:
Click on “Run code snippet” -> “My Website” to see the result
const userWebsite = "data:text/html;base64,PHNjcmlwdD5hbGVydCgiSGFja2VkISIpOzwvc2NyaXB0Pg==";
class UserProfilePage extends React.Component {
render() {
const url = userWebsite.replace(/^(javascript\:)/, "");
return (
<a href={url}>My Website</a>
)
}
}
ReactDOM.render(<UserProfilePage />, document.querySelector("#app"));<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="app"></div>3. XSS via attacker controlled props
const customPropsControledByAttacker = {
dangerouslySetInnerHTML: {
"__html": "<img onerror="alert(\"Hacked!\");" src="https://stackoverflow.com/questions/33644499/invalid-image" />"
}
};
class Divider extends React.Component {
render() {
return (
<div {...customPropsControledByAttacker} />
);
}
}
ReactDOM.render(<Divider />, document.querySelector("#app"));<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/react/15.1.0/react-dom.min.js"></script>
<div id="app"></div>Here are more resources