[Pragyan CTF] Roller Coaster Ride

Standard

Description:

Bobby has been into Reverse Engineering and Binary Exploitation lately.
One day, he went to an amusement park in his city. It was very famouse for its Roller Coaster Rides.
But, Bobby, being 12 years old, was not allowed on those rides, as it was open for people who were 14 years or older.
This made Bobby very angry. On reaching home, he hacked into the servers of the amusement park, got hold of the validation software for the Roller Coaster rides, and modified it, so that nobody is allowed to have a ride on those Roller Coasters.

validation

 

We are given with a file, lets run file command on it determine its type.

Okay, it’s an ELF file. Lets execute it:

 

Okay let’s disassemble the file and look at the functions call tree:

Oh, we have lot of functions. All of them looks something like this:

An hex value is moved to r9 (smetimes r8) and then xord with hex value that was moved to rax. I manually xord all the values by order of calls, turn the results to characters and end up with the flag:

The flag was pragyanctf{r01l+th3m_411-up/@nd~4w@y}

2 thoughts on “[Pragyan CTF] Roller Coaster Ride

  1. Parth

    What tool did you use to generate the call graph? While solving the challenge I found it hard to go through all the jumps manually. Was wondering if there’s a tool to display that nicely.

    • Megabeets

      Hey, I used IDA Pro. You can start from the function “f1” and keep jumping between the functions while you don’t forget to note the XORs.

Leave a Reply

Your email address will not be published. Required fields are marked *