# performance.now + Force heavy task
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**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
```
Learn AWS hacking from zero to hero with htARTE (HackTricks AWS Red Team Expert)!
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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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