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60 lines
4.2 KiB
Markdown
60 lines
4.2 KiB
Markdown
# Blocking main page to steal postmessage
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{% hint style="success" %}
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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">\
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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)
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<details>
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<summary>Support HackTricks</summary>
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* Check the [**subscription plans**](https://github.com/sponsors/carlospolop)!
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* **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)**.**
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* **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.
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</details>
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{% endhint %}
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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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{% hint style="success" %}
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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">\
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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)
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<details>
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|
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<summary>Support HackTricks</summary>
|
|
|
|
* 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)**.**
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* **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.
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</details>
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{% endhint %}
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