Ali Al Balushi

Ali Al Balushi

2 minute read



Writeup Overview – ZEXOR v0.1 Target

  • Name: ZEXOR v0.1
  • Author: svidnet
  • Platform: Windows
  • Architecture: x86-64
  • Language: C / C++
  • Difficulty: 1.0 (Beginner) 🟢
  • Quality: 4.5 ⭐
  • Upload Date: 2025-12-30
  • Description: ZEXOR v0.1 is a basic license checker designed for beginners

First, I run the exe file:

target

It asks for a License Key.

Next, I start with the IDA pro tool by opening the exe inside it, then locating CheckLicense() from the function window:

CheckLicense() function

We can see the strcmp() call. As we know, on x64 Windows, strcmp handles parameters like this:

  • RCX reg for user input.
  • RDX reg for another located resource (which is the expected licence).

So our focus on the RDX

  • The RDX assigning:

rdx line

  • So RDX is assigned to cs:LICENO, and cs indicates that LICENO is a global variable.

Let's navigate to the LICENO

LICENO Pointer

As we can see here, the LICENO is a pointer pointing to the address holding the license key (dq or Quadword which represents an address in an x64 system).

And here is the License:

the License

proof