– – Program Information

This post will be more about how I developed this, since the solution is fairly straight forward once you know how it’s implemented. The idea came to me while my boyfriend, Chris, was playing a game on Steam Link. Due to an odd bug, while playing Dark Souls, the Steam Link kept shutting off.
ctf exe

What is a CTF Loader (ctfmon.exe)?

This post will be more about how I developed this, since the solution is fairly straight forward once you know how it’s implemented. The idea came to me while my boyfriend, Chris, was playing a game on Steam Link. Due to an odd bug, while playing Dark Souls, the Steam Link kept shutting off. Eventually, we realized that even though the game was running, the Steam menu was still “in focus”.

That means that while he was playing the game, he was also moving around and clicking things on the menu. Very reminiscent of Clickjacking attacks.

I tried to figure out something I could do with this, and slept on it. The next day, I had an idea: I’d write a backdoor into Windows Calculator such that, when a special code was entered, it’d decrypt and display the flag. Just like Steam Link, you’d be entering the code in the background as you’re doing calculations. I really wanted some Windows reverse engineering challenges, not to mention oldschool software references, so this was perfect!

You can grab the patched binary and try it out, if you like! Getting calc. I found the place where I wanted to add the custom code, then made a small change to make sure it’d work, and it started crashing immediately.

Even changing a simple string prevented it from starting. I quickly gave up on that. I decided to use Windows instead. I had no idea how Windows was packaged, so I just mounted the iso: What’s calc. Apparently I already had cabextract installed, so I tried it: You can download the base calc. Finding a place for code I spent a lot of time coming up with ideas of how to backdoor calc. I could have used a tool like Backdoor Factory , but that wasn’t quite right!

I also had the idea of using debug hooks and causing exceptions to gain control, but I couldn’t get that to work. Instead, I decided to find a place right in the binary where I could put a decent chunk of assembly code – like bytes or so – that could handle all the logic.

Then I’d just find the part of the code that handles “button pressed”, and call my backdoor code. That way, each button press, I could do some arbitrary calculation, then return control as if nothing had ever happened. The question is, where? How do I spot useless code? In particular, in an executable segment? I just wrecked up built-in security functionality. I scrolled around for awhile, trying to think of where to put it.

Then I noticed this: Who the heck needs a stack cookie for Windows Calculator, right? What are you going to do, hack yourself? So I went ahead and changed the first byte of the function 0xE2C is the virtual address, or 0xc in the file to 0xc3 – ret. Then I ran calc. In theory, it’s slightly less secure – hah. The rest of the function – 0xE2D up to 0xEC9 bytes – was now entirely unused. There are plenty of easier ways to do this – such as by decrypting it on the stack – but this seemed easy enough to do.

I also needed a smaller piece of unused memory to store the count which is incremented each time the correct button is pressed – we’ll see that later.

In the start function, I noticed this code: While writing this blog, I actually looked up what initterm is , and realized that it isn’t even doing anything – it just points to two NULL addresses.

So I went ahead and NOP’ed out that code, so those two memory addresses would remain untouched. Then I set the value at that address to 0x, to initialize the counter although I think it already had that value. For the actual flag, I had to store it in UTF, so if I wanted a 16 character flag, I needed 32 bytes of memory to store it in. That’s a lot! I solved that problem by overwriting random unused-looking chunks of memory until calc.

Probably not the cleanest solution – I may have redefined math as we know it – but it did the trick! That memory ended up starting here: I initialized that to the “encrypted” version of the flag, which is simply the 32 byte flag XORed by the values for certain calculator buttons – we’ll see that later. This could certainly have been done more easily, but I was finding memory as I needed it, so it became somewhat complex.

Since this is a reverse engineering problem, that makes it all the more fun! Find where button presses are handled Now that we have space for code, how do we run the code? I wish I had a good story about how to find the code. In the Windows 7 version of calc. But the Windows 7 version didn’t work, and Windows didn’t have symbols. In the end, I literally just sorted the list of functions by length, and looked at the longest one: The body of that sub looks like: Compare, jump, compare, jump, compare jump, etc.

That looks like buttons being checked! The value being compared at each step is stored in esi, which is defined at the top of that function: I used r esi to see the argument: Now that I know where button-pushes are processed, I know where I need to inject my code! I assume it’s part of the “this execution is taking too long” code, since that stopped working when I added this patch.

But we fix that later. The first byte of the original call – E8 – simply means “call a 4-byte relative address”. The next 4 bytes are the offset from the start of the next instruction to the instruction we want to call as little endian. What’s that mean? It means that we need to know how far it is from the next instruction 0xAB and the place we want to call 0xE2D. We can figure that out with simple math: Of course, right now there’s just the remnants of the old function there, so if you call it, it’ll crash.

That brings us to the last major part – the payload! Payload The payload is the most important part! It’s simply arbitrary assembly code that’ll run each time a button is pressed. The way it works is, it takes the button code such as 0x7c for ‘0’ and compares it to the current byte of the expected code starting at offset 0.

If it doesn’t match, we reset the counter and return. If it does match, we increment the counter and return if the counter is less than 8. When the counter reaches 8 – the length of the code – it runs the “decryption” code and pops up a MessageBox with the decrypted flag. The decryption code will XOR the first 4 bytes of the encrypted flag with the first byte of the code. The next 4 bytes with the next byte, and so on, until the 8 code bytes have decoded the 32 flag bytes.

Don’t do that if you want real security! Here’s the full, annotated assembly: That means we need to use 2 bytes for every character of our flag.

Why do we use that one? Because it’s what calc. In the patch. Here’s what it looks like when I run the generator script: All said and done, the patch is bytes long with no real attempt to optimized my assembly. Not too shabby! Fixing “this calculation is taking too long” One funny thing – I was forever getting “This calculation is taking too long, would you like to continue?

I tracked down the code to display it, and figured out it runs in a separate thread: CreateThread By this point, I just wanted to go to bed I wrote this whole thing in one evening! That thread no longer runs, and my problem is solved. I still have no idea why I started seeing that..

Putting it all together All said and done, here are all the patches I just talked about, all in one place: Eight patches, and we have a cool backdoor in Calc! The coolest thing is, the flag and code are both generated dynamically.

That means you can easily change the code and data and get your own encrypted flag!

CTF.EXE Information

The file is related to the CTF (Collaborative Translation Framework) Loader. This is a service that is used to provide text support for. Greetings fellow hackers. I’ve been playing some binary CTFs earlier so I decided to play reversing challenges. Key to understand this. [UPDATED] What’s CTF Loader? Learn what is and how to disable it with this easy tutorial. Is CTF Loader harmful? Find out now!.

Come Across CTF Loader Issue On Windows 10? Fix It Now [MiniTool News]

What is a CTF Loader ctfmon. This post continues our series of articles about Windows processes and today we will discuss what is CTF loader Collaborative Translation Framework or ctfmon. This component is responsible for Alternative User Input and Office language panel.

Finding a place for code

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VIDEO: What is a CTF Loader (

This post continues our series of articles about Windows processes and today we will discuss what is CTF loader (Collaborative Translation Framework) or, how can user disable it and if it’s safe. (CTF loader) is a Windows system component which appeared in. The, or CTF Loader, opens on the startup of the Windows operating system and it is running in the background. This service may be. This entry has information about the startup entry named that points to the file. This program should not be allowed to start. Please visit this result.

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