Someone who doesn’t care about bandwidth usage decided to package both the server and client binaries in a single file… The server of course is meant to run on linux, and the client on Windows.

We get a PowerShell file eulers_license.ps1 that contains:

  • a binary_linux var containing the server code encoded in base64.
  • a binary_win var containing the client code also encoded in base64.

The linux binary

The linux binary is very easy to reverse. In fact by decoding it we get a python server which has a huge SQLi vuln:

lice = request.args.get("license_key")
query = "SELECT * FROM license_keys WHERE license_key = '" + lice + "';"

we can proceed with a basic SQLi like ' OR 1=1 -- and get the first part of the flag (which is the second one really):


The windows binary

The windows exe is a little bit harder to reverse. By looking at it with ghidra we understand that it must be:

  • a 10 digits number
  • a prime number
  • it has something to do with Euler

By a combination of chance and testing we come across the number 2147483647 which is a prime number discovered by Euler.

Providing this input to the client gives us the output:

Enter eulers license key: 2147483647
Failed to contact for license confirmation...