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Firmware is essential software that enables devices to operate correctly by managing and facilitating communication between the hardware components and the software that users interact with. It's stored in permanent memory, ensuring the device can access vital instructions from the moment it's powered on, leading to the operating system's launch. Examining and potentially modifying firmware is a critical step in identifying security vulnerabilities.
## **Gathering Information**
**Gathering information** is a critical initial step in understanding a device's makeup and the technologies it uses. This process involves collecting data on:
* The CPU architecture and operating system it runs
* Bootloader specifics
* Hardware layout and datasheets
* Codebase metrics and source locations
* External libraries and license types
* Update histories and regulatory certifications
* Architectural and flow diagrams
* Security assessments and identified vulnerabilities
For this purpose, **open-source intelligence (OSINT)** tools are invaluable, as is the analysis of any available open-source software components through manual and automated review processes. Tools like [Coverity Scan](https://scan.coverity.com) and [Semmle’s LGTM](https://lgtm.com/#explore) offer free static analysis that can be leveraged to find potential issues.
## **Acquiring the Firmware**
Obtaining firmware can be approached through various means, each with its own level of complexity:
* **Directly** from the source (developers, manufacturers)
* **Building** it from provided instructions
* **Downloading** from official support sites
* Utilizing **Google dork** queries for finding hosted firmware files
* Accessing **cloud storage** directly, with tools like [S3Scanner](https://github.com/sa7mon/S3Scanner)
* Intercepting **updates** via man-in-the-middle techniques
* **Extracting** from the device through connections like **UART**, **JTAG**, or **PICit**
* **Sniffing** for update requests within device communication
* Identifying and using **hardcoded update endpoints**
* **Dumping** from the bootloader or network
* **Removing and reading** the storage chip, when all else fails, using appropriate hardware tools
## Analyzing the firmware
Now that you **have the firmware**, you need to extract information about it to know how to treat it. Different tools you can use for that:
```bash
file <bin>
strings -n8 <bin>
strings -tx <bin>#print offsets in hex
hexdump -C -n 512 <bin> > hexdump.out
hexdump -C <bin> | head # might find signatures in header
fdisk -lu <bin>#lists a drives partition and filesystems if multiple
```
If you don't find much with those tools check the **entropy** of the image with `binwalk -E <bin>`, if low entropy, then it's not likely to be encrypted. If high entropy, Its likely encrypted (or compressed in some way).
Moreover, you can use these tools to extract **files embedded inside the firmware**:
Or [**binvis.io**](https://binvis.io/#/) ([code](https://code.google.com/archive/p/binvis/)) to inspect the file.
### Getting the Filesystem
With the previous commented tools like `binwalk -ev <bin>` you should have been able to **extract the filesystem**.\
Binwalk usually extracts it inside a **folder named as the filesystem type**, which usually is one of the following: squashfs, ubifs, romfs, rootfs, jffs2, yaffs2, cramfs, initramfs.
#### Manual Filesystem Extraction
Sometimes, binwalk will **not have the magic byte of the filesystem in its signatures**. In these cases, use binwalk to **find the offset of the filesystem and carve the compressed filesystem** from the binary and **manually extract** the filesystem according to its type using the steps below.
Files will be in "`squashfs-root`" directory afterwards.
* CPIO archive files
`$ cpio -ivd --no-absolute-filenames -F <bin>`
* For jffs2 filesystems
`$ jefferson rootfsfile.jffs2`
* For ubifs filesystems with NAND flash
`$ ubireader_extract_images -u UBI -s <start_offset> <bin>`
`$ ubidump.py <bin>`
## Analyzing Firmware
Once the firmware is obtained, it's essential to dissect it for understanding its structure and potential vulnerabilities. This process involves utilizing various tools to analyze and extract valuable data from the firmware image.
### Initial Analysis Tools
A set of commands is provided for initial inspection of the binary file (referred to as `<bin>`). These commands help in identifying file types, extracting strings, analyzing binary data, and understanding the partition and filesystem details:
```bash
file <bin>
strings -n8 <bin>
strings -tx <bin>#prints offsets in hexadecimal
hexdump -C -n 512 <bin> > hexdump.out
hexdump -C <bin> | head #useful for finding signatures in the header
fdisk -lu <bin>#lists partitions and filesystems, if there are multiple
```
To assess the encryption status of the image, the **entropy** is checked with `binwalk -E <bin>`. Low entropy suggests a lack of encryption, while high entropy indicates possible encryption or compression.
For extracting **embedded files**, tools and resources like the **file-data-carving-recovery-tools** documentation and **binvis.io** for file inspection are recommended.
### Extracting the Filesystem
Using `binwalk -ev <bin>`, one can usually extract the filesystem, often into a directory named after the filesystem type (e.g., squashfs, ubifs). However, when **binwalk** fails to recognize the filesystem type due to missing magic bytes, manual extraction is necessary. This involves using `binwalk` to locate the filesystem's offset, followed by the `dd` command to carve out the filesystem:
Afterwards, depending on the filesystem type (e.g., squashfs, cpio, jffs2, ubifs), different commands are used to manually extract the contents.
### Filesystem Analysis
With the filesystem extracted, the search for security flaws begins. Attention is paid to insecure network daemons, hardcoded credentials, API endpoints, update server functionalities, uncompiled code, startup scripts, and compiled binaries for offline analysis.
**Key locations** and **items** to inspect include:
* **etc/shadow** and **etc/passwd** for user credentials
* SSL certificates and keys in **etc/ssl**
* Configuration and script files for potential vulnerabilities
* Embedded binaries for further analysis
* Common IoT device web servers and binaries
Several tools assist in uncovering sensitive information and vulnerabilities within the filesystem:
* [**LinPEAS**](https://github.com/carlospolop/PEASS-ng) and [**Firmwalker**](https://github.com/craigz28/firmwalker) for sensitive information search
* [**The Firmware Analysis and Comparison Tool (FACT)**](https://github.com/fkie-cad/FACT\_core) for comprehensive firmware analysis
* [**FwAnalyzer**](https://github.com/cruise-automation/fwanalyzer), [**ByteSweep**](https://gitlab.com/bytesweep/bytesweep), [**ByteSweep-go**](https://gitlab.com/bytesweep/bytesweep-go), and [**EMBA**](https://github.com/e-m-b-a/emba) for static and dynamic analysis
### Security Checks on Compiled Binaries
Both source code and compiled binaries found in the filesystem must be scrutinized for vulnerabilities. Tools like **checksec.sh** for Unix binaries and **PESecurity** for Windows binaries help identify unprotected binaries that could be exploited.
## Emulating Firmware for Dynamic Analysis
The process of emulating firmware enables **dynamic analysis** either of a device's operation or an individual program. This approach can encounter challenges with hardware or architecture dependencies, but transferring the root filesystem or specific binaries to a device with matching architecture and endianness, such as a Raspberry Pi, or to a pre-built virtual machine, can facilitate further testing.
### Emulating Individual Binaries
For examining single programs, identifying the program's endianness and CPU architecture is crucial.
#### Example with MIPS Architecture
To emulate a MIPS architecture binary, one can use the command:
For MIPS (big-endian), `qemu-mips` is used, and for little-endian binaries, `qemu-mipsel` would be the choice.
#### ARM Architecture Emulation
For ARM binaries, the process is similar, with the `qemu-arm` emulator being utilized for emulation.
### Full System Emulation
Tools like [Firmadyne](https://github.com/firmadyne/firmadyne), [Firmware Analysis Toolkit](https://github.com/attify/firmware-analysis-toolkit), and others, facilitate full firmware emulation, automating the process and aiding in dynamic analysis.
## Dynamic Analysis in Practice
At this stage, either a real or emulated device environment is used for analysis. It's essential to maintain shell access to the OS and filesystem. Emulation may not perfectly mimic hardware interactions, necessitating occasional emulation restarts. Analysis should revisit the filesystem, exploit exposed webpages and network services, and explore bootloader vulnerabilities. Firmware integrity tests are critical to identify potential backdoor vulnerabilities.
## Runtime Analysis Techniques
Runtime analysis involves interacting with a process or binary in its operating environment, using tools like gdb-multiarch, Frida, and Ghidra for setting breakpoints and identifying vulnerabilities through fuzzing and other techniques.
## Binary Exploitation and Proof-of-Concept
Developing a PoC for identified vulnerabilities requires a deep understanding of the target architecture and programming in lower-level languages. Binary runtime protections in embedded systems are rare, but when present, techniques like Return Oriented Programming (ROP) may be necessary.
## Prepared Operating Systems for Firmware Analysis
Operating systems like [AttifyOS](https://github.com/adi0x90/attifyos) and [EmbedOS](https://github.com/scriptingxss/EmbedOS) provide pre-configured environments for firmware security testing, equipped with necessary tools.
## Prepared OSs to analyze Firmware
* [**AttifyOS**](https://github.com/adi0x90/attifyos): AttifyOS is a distro intended to help you perform security assessment and penetration testing of Internet of Things (IoT) devices. It saves you a lot of time by providing a pre-configured environment with all the necessary tools loaded.
* [**EmbedOS**](https://github.com/scriptingxss/EmbedOS): Embedded security testing operating system based on Ubuntu 18.04 preloaded with firmware security testing tools.
## Vulnerable firmware to practice
To practice discovering vulnerabilities in firmware, use the following vulnerable firmware projects as a starting point.
* [Practical IoT Hacking: The Definitive Guide to Attacking the Internet of Things](https://www.amazon.co.uk/Practical-IoT-Hacking-F-Chantzis/dp/1718500904)
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