TheReturnOfTheInts

A reverse engineering crackme written in C, designed as a HackTheBox-style challenge.

Description

A password-protected binary that validates your input and returns a flag if correct. Sounds simple. It isn't.

Challenge

Reverse engineer the binary to find the correct password. The flag will be printed in HTB{...} format upon success.

Building

make all

Dependencies: OpenSSL (libssl-dev)

# Ubuntu/Debian
sudo apt install libssl-dev

Concepts Covered

• Anti-debugging techniques (ptrace)
• Multi-threaded execution and race condition analysis
• MD5 hashing
• Byte-level XOR obfuscation
• Loop-based value obfuscation
• Function pointer obfuscation
• Red herring analysis

Hints

Hint 1

The program detects debuggers. How does it do that, and can it be bypassed?

Hint 2

The password is assembled across multiple threads. What does each thread actually contribute?

Hint 3

Not everything that looks random is random. Trace the math.

Hint 4

The password is never stored as plaintext. What is it compared against?

Recommended Tools

• GDB with pwndbg
• Ghidra or IDA
• Python for scripting
• ltrace / strace

Author

Andromeda1957 — github.com/Andromeda1957

HTB: andromeda1957 — Prodigy rank, 186 machines rooted

See also: Reversing-Challenges for more RE practice material.