How I Cracked Password Without Knowing It | strncmp Bug Explained | Google CTF (BEGINNER'S QUEST)

In this CTF write-up I solve "Guess Password Hard" (Google CTF BEGINNER'S QUEST) — a challenge that seems impossible because the password has 26^15 possible combinations. But instead of guessing, we find a single bug in the C++ source code that lets us win in about 4 minutes. The bug: strncmp() is used to compare SHA256 hashes. SHA256 output is raw binary data, not a C string — so strncmp stops at the first null byte (0x00) it finds. About 1 in 256 rounds, the server's hash starts with 0x00. We submit a password whose hash also starts with 0x00, and strncmp returns 0 (equal) without checking the rest. Flag captured. 📚 What you'll learn How SHA256 hashing works Why strncmp is dangerous on binary data How to read C/C++ source code for vulnerabilities Writing a Python exploit script from scratch #CTF #CyberSecurity #EthicalHacking Follow me on Instagram :-   / kushgo13   Follow me on Tweeter :-   / kushgo13