631 reads

Creating Cheats for Dead Cells Using Unsafe Rust

by Matěj SmyčkaNovember 22nd, 2023

Too Long; Didn't Read

The Dead Cells game uses cells as currency for unlocking new items. I will try to change the cell value to some arbitrary number. We have multiple possible approaches to changing cell value. I chose an external memory manipulation cheat because it does not require changes in the original binary.

featured image - Creating Cheats for Dead Cells Using Unsafe Rust

In this guide, we'll explore the process of creating a cheat for the popular game Dead Cells. The intention behind this guide is purely educational, and I do not endorse cheating for malicious purposes. With that out of the way, let's dive in.

First, I wanted to create a guide on creating a cheat for Wesnoth, but I found that somebody has already done it and described it in this excellent learning resource[1].

Source code: https://github.com/matejsmycka/cell-generator

Approach

The Dead Cells game uses cells as currency for unlocking new items. With each run, you start with 0 cells.

I will try to change the cell value to some arbitrary number.

We have multiple possible approaches to changing cell value:

Code Caves
DLL injection
External cheat

I chose an external memory manipulation cheat because it does not require changes in the original binary, which Steam could recognize. Now that we have chosen the approach, we need to define the necessary steps to perform to get a persistent cheat.

Find the dynamic address of a cell counter.
Get static values that point to our dynamic address.
Create a program in Rust that automates the process.

Finding a dynamic address using Cheat Engine

"Cheat Engine is by far the de facto "industry standard" for GamePwn. It bundles together essentially every possible tool that could be required into one neat little package."[2] - PandaSt0rm

We can attach CheatEngine to our running DeadCells game. To get relevant dynamic addresses, you need to play the game, get some cells, and then scan for new values in memory. We don't know the type of value we are looking for, but it will likely be a number. After a few scans, you are left with multiple addresses that seem relevant.

Try modifying values to see if it changes in-game value. However, to update the game GUI, you need to play and get or spend some cells; changing its memory doesn't update the game GUI counter.

And voila, the cell counterchanged. But this is not persistent. We need to perform a pointer scan to get reliable pointers.

Defeating dynamic memory allocation (DMA)

Because modern operating systems use DMA, we have to find a location that doesn't disappear after restarting the process.

We will use another CheatEngine feature, pointerscanner to get a static pointer.

A good resource on how to use pointerscanner is here unknowncheats.me.

In order to find out static clues to dynamic location, you need to:

locate dynamic address
perform pointerscan
close game
open game
load the last pointerscan and look for the value of the cell counter.
repeat steps 3-5 until you get a reliable multilevel pointer.

It consists of the base address of some game modules, for example, Kernel32.dll+0x00048184and multiple static values called offsets. Now, we have multiple values which point to our dynamic memory location.

Unsafe rust

I chose Rust language because a lot of resources are written in C++, which is similar. However, I consider writing Rust more fun than writing it in C++. Python is also a solid option.

After trying multiple libraries, I chose to go with a library named toy-arms[3].

This lib is sort of a wrapper around low-level memory and process functions, so I don't have to use Windows Foreign Function Interface (FFI) directly. I ended up with the following script.

The code can be found here.

Here is pseudocode, which explains individual steps.

function main():
    proc = getProcessByName("deadcells.exe")
    client = proc.getModuleInfo("libhl.dll")
    moduleAddr = client.baseAddress + 0x00048184
    offsets = [0x6B8, 0x4, 0x18, 0x68, 0x480, 0xC, 0x358]

    cellCounterPtr = followPointerChain(moduleAddr, offsets)
    cellCounterValue = readMemory(cellCounterPtr)
    newValue = 99999
    writeMemory(cellCounterPtr, newValue)

And below is the actual code of main.

fn main() {
    let proc;
    match Process::from_process_name("deadcells.exe") {
        Ok(p) => proc = p,
        Err(e) => {
            println!("{}", e);
            return;
        }
    }
    let client: Module;
    match proc.get_module_info("libhl.dll") {
        Ok(m) => client = m,
        Err(e) => {
            println!("{}", e);
            return;
        }
    }

    let module_addr = client.base_address + 0x00048184;
    let offsets = [0x6B8, 0x4, 0x18, 0x68, 0x480, 0xC, 0x358].to_vec();

    let cell_counter_ptr: usize = follow_ptr_chain_u32(&proc, module_addr, &offsets);
    let mut cell_counter_value: u32 = 0;
    let _ = read(
        &proc.handle,
        cell_counter_ptr as usize,
        size_of::<u32>(),
        &mut cell_counter_value as *mut u32,
    );

    println!("Current cell counter value: {:?}", cell_counter_value);
    println!("Enter a new value:");
    let mut input = String::new();
    io::stdin()
        .read_line(&mut input)
        .expect("Failed to read line");
    let mut new_value: u32 = input.trim().parse().unwrap();
    let new_value_ptr = &mut new_value;
    let _ = write(&proc.handle, cell_counter_ptr, new_value_ptr);
    println!("Cell counter UI will be updated after sub/add cell ingame event.")
}

NOTE: Due to endianness, reverse your offsets found by CheatEngine.

After compiling and running the Rust binary, the Powershell window will pop up.

Possible improvements:

Some nice GUI could be implemented (for easier usage), or other in-game values could be changed, like the freezing value of health, but these are rather simple implementations, considering that the main logic was implemented.

Wrap-up

Writing in Python with libraries like pyMeow[4] would be easier, but Rust libraries' low-level and non-mature nature made me understand it in more detail. Game hacking is a great intro to Windows API. As a Linux guy, I recommend trying something similar for everybody.