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Firmware Analysis with binwalk

Updated: Jan 12, 2023

When it comes to reverse engineering firmware images, binwalk is truly a tool of its own class. But what exactly is binwalk and how can it help in the process of reverse engineering? In this blog, we will discuss what binwalk is, why it can be quite useful when trying to reverse engineer a firmware image, and what tips and tricks you should consider when using it.


What is Binwalk?

Binwalk is a tool for reverse engineering static and dynamic binaries and firmware images. It does this through manual inspection or automated analysis and is often referred to as a firmware reversing tool. It works by scanning a binary or firmware image and then identifying its structure. Once the internal structure of the binary or firmware is identified, binwalk provides the user with a great deal of insight into what may be contained within the binary, such as the various components it may contain, such as executable code or static data.


Binwalk has been designed with a modular architecture and is capable of extracting firmware contents such as kernel images, library files and root filesystems.


Why Use Binwalk?

Binwalk is an incredibly powerful and useful tool when it comes to reverse engineering firmware images. It provides users the ability to easily identify the contents of firmware images and view the filesystem image contained within. With the data recovered from the firmware, users can then extract the components contained within, such as root filesystems and kernels. This provides users with the ability to study the inside of firmware and make changes and modifications to it, as well as better understand exactly how the firmware works.


Furthermore, Binwalk can produce detailed results as to the contents and structure of binaries and firmware images without actually running them. This is especially useful for those attempting to reverse engineer firmware images, as it allows users to inspect the internals of the image without actually having to run it.


Tips and Tricks for Using Binwalk

When using binwalk, it can be incredibly helpful to use the command-line version of the tool as it provides more options when scanning. The command-line version also allows users to combine two or more tools for more detailed analysis of the target binary or firmware.


When using binwalk, it is also important to be mindful of the entire content of the binary or firmware image. Binwalk can be used to scan entire lengths of firmware and identify contents such as kernel images, filesystem images, libraries, and executables. In order to get the most detailed results, it is important to scan the entire length of the binary or firmware image.


Another tip to keep in mind when using binwalk to reverse engineer a firmware image is to start off with a smaller segment of the binary first. This way, users can start to get a sense of the internal structure of the firmware and can then gradually expand the area of the binary being scanned.


Example Commands to Show Binwalk’s Usage

In this section, we will provide some example commands to show how binwalk can be used to reverse engineer a firmware image. We will assume the following information. The target firmware image is located at /my-firmware.bin


First, let’s take a look at the basic command used to scan an image:


binwalk /my-firmware.bin


This will scan the image and provide a detailed report of all the components that may be contained within the image.


Another useful command is to extract all of the contents from the firmware image:


binwalk -e /my-firmware.bin


This will extract the contents of the image and store the extracted files in a folder created in the current directory.


Finally, for detailed inspection of the binary and firmware, we can use a combination of two or more tools:


binwalk -M /my-firmware.bin


This command will scan the binary with both binwalk and some other tools, providing even greater insight into the internals of the firmware image.


Conclusion

In conclusion, binwalk is an extremely powerful tool when it comes to reverse engineering firmware images. It is incredibly helpful in identifying the structure and components of the image and can be used with other tools to provide users with even greater insight into the internals. By following the tips and tricks outlined in this blog, users will be well prepared to take on the task of reverse engineering firmware images with binwalk.


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