Scratch_Space

by hoover Reverse Engineering beginner New to reverse engineering? This beginner challenge is an introduction to inspecting the memory of a running Linux program with a debugger.

The provided x86-64 ELF asks you to guess a passphrase. The passphrase is the flag, and this time it is never stored on disk and never passed to a library function. The program maps a scratch page, builds the real passphrase there, compares it against your guess with a loop of its own, then zeroes the page and unmaps it before printing anything. strings, ltrace and strace all come back empty.

We recommend using pwndbg, a GDB extension commonly used for pwn challenges. Its telescope command can help you inspect the pointer and the memory it points to before the program wipes it.