Hack.lu CTF 2017 Indianer Write Up
This is a writeup of the Indianer challenge from Hack.lu 2017
The challenge was tagged Web/Pwn.
Initially, the challenge included a binary and a link to a regular website that had a "super secret" backdoor.
After downloading and unzipping, we noticed the .so file header on the binary, indicating that it was a shared object. This meant it was a small part of a code base that we did not have access to. There was also nothing that could be executed within the file meaning dynamic analysis was not a plausible strategy. Fortunately, after opening the file in Binary Ninja we uncovered a few key points that brought forth some clarity.
The binary was loaded before libc to overwrite the strlen function. Analyzing the control flow of strlen revealed the abnormality and exploit.
