# performance.now + Force heavy task {% hint style="success" %} Learn & practice AWS Hacking:

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{% endhint %} **Exploit taken from** [**https://blog.huli.tw/2022/06/14/en/justctf-2022-xsleak-writeup/**](https://blog.huli.tw/2022/06/14/en/justctf-2022-xsleak-writeup/) In this challenge the user could sent thousands of chars and if the flag was contained, the chars would be sent back to the bot. So putting a big amount of chars the attacker could measure if the flag was containing in the sent string or not. {% hint style="warning" %} Initially, I didn’t set object width and height, but later on, I found that it’s important because the default size is too small to make a difference in the load time. {% endhint %} ```html

``` {% hint style="success" %} Learn & practice AWS Hacking:

[**HackTricks Training AWS Red Team Expert (ARTE)**](https://training.hacktricks.xyz/courses/arte)

\ Learn & practice GCP Hacking:

[**HackTricks Training GCP Red Team Expert (GRTE)**

](https://training.hacktricks.xyz/courses/grte)

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