Rating: 5.0

# Parrot

## Vulnerability
- Information leak
- Write is not be terminate by null byte
- It can leak some data on the heap

- A null byte overwrite
- If you give a large size,it would read faild.
- But it's not check and it would put a null byte to the address.

## Exploit
- Leak libc
- Create a unsorted bin on the heap
- Using the vulnerability to leak data
- Overwrite the last byte of `_IO_buf_base` with null byte in the stdin structure
- The pointer point to `_short_buf` which in the stdin structure at first
- You will have a stdin buffer in stdin structure
- If we use any stdin related functions, we could overwrite `_IO_buf_end`
- Overwrite `_IO_buf_base` and `_IO_buf_end`
- Use `scanf` to read data
- It's can control the stdin buffer then you can write to arbitrary memory
- Overwrite `__free_hook`
- Control the flow
- [exploit](parrot.py)

Original writeup (https://github.com/scwuaptx/CTF/blob/master/2017-writeup/twctf/Parrot.md).