input_checker

[Input Checker]

Summary

• Stack Overflow

Tools

• pwndbg
• IDA Pro 7.0

Description

• Vulnerability

  • 
  • It's just stack overflow.
  • Notice that int j is the index of input array.
    • Could change the return address by overwriting int j.
    • offset = 0x628 - 0x210 = 0x418

• Exploit

  • Just changed the return address to 0x401253.

    0x401253:   mov    edx,0x0
    0x401258:   mov    esi,0x0
    0x40125d:   lea    rdi,[rip+0xdae]        # 0x402012
    0x401264:   call   0x4010a0 <execve@plt>

  • ex.py

• IJCTF{1nt3r3st1ng_e3sY-s0lut10ns_ex1sTz!}