We are given 2 options Login and Join. We certainly can't login, so we have to join. Unlucky for us Javascript blocks us from Join. If we inspect login we are redirected to https://webhacking.kr/challenge/web-05/mem/login.php and lucky for us if we visit /join.php we get a page.
let a = 'a';
let b = 'b';
let c = 'c';
let d = 'd';
let e = 'e';
let f = 'f';
let g = 'g';
let h = 'h';
let i = 'i';
let j = 'j';
let k = 'k';
let l = 'l';
let m = 'm';
let n = 'n';
let o = 'o';
let p = 'p';
let q = 'q';
let r = 'r';
let s = 's';
let t = 't';
let u = 'u';
let v = 'v';
let w = 'w';
let x = 'x';
let y = 'y';
let z = 'z';
let _1 = '1';
let _2 = '2';
let _3 = '3';
let _4 = '4';
let _5 = '5';
let _6 = '6';
let _7 = '7';
let _8 = '8';
let _9 = '9';
let _0 = '0';
let dot = '.';
let lt = '<';
let gt = '>';
let oldzombie = o + l + d + z + o + m + b + i + e;
let document_cookie = d + o + c + u + m + e + n + t + dot + c + o + o + k + i + e;
if (eval(document_cookie).indexOf(oldzombie) == -1) {
alert('bye');
throw "stop";
}
if (eval(d + o + c + u + m + e + n + t + dot + 'U' + 'R' + 'L').indexOf(m + o + d + e + '=' + _1) == -1) {
alert('access_denied');
throw "stop";
} else {
document.write('<font size=2 color=white>Join</font><p>');
document.write('.<p>.<p>.<p>.<p>.<p>');
document.write('<form method=post action=' + j + o + i + n + dot + p + h + p + '>');
document.write('<table border=1><tr><td><font color=gray>id</font></td><td><input type=text name=' + i + d + ' maxlength=20></td></tr>');
document.write('<tr><td><font color=gray>pass</font></td><td><input type=text name=' + p + w + '></td></tr>');
document.write('<tr align=center><td colspan=2><input type=submit></td></tr></form></table>');
}
