Dobby2

What is Dobby?

Dobby is a hobby project I have created to help me reverse engineer a few highly obfuscated binaries.

Dobby is an emulator that provides interesting tools like a symbolic API, reverse taint analysis, multiple emulation engines, snapshots, and quick prototyping.

The tool is built upon a set of "providers" that work as backends. Currently the two providers include Triton and Unicorn. (See dobby_unicorn.py and dobby_triton.py) Having multiple different engines with different strengths share an environment is a big advantage.

Other providers can be added simply by implementing the portions of an API that they can. (See interface.py)

Features

• Kernel-mode Emulation
• x86_64 emulation
• Concolic Execution
• Reverse Taint Analysis
• Snapshotting
• Multiple Backends
• Execution Hooks
• Read/Write hooks
• Memory Annotations
• Instruction Trace Comparisons

Q & A

How does this tool help defeat strong obfuscation?

One of the best ways to deobfuscate a binary is to ignore it's obfuscations and just watch for it's side effects. As long as a target binary does not know it is being emulated this can reveal a lot of information. However there is always the fear that the binary has detected it is being watched, and will act differently. Both differential execution and symbolic execution help Dobby find and mitigate the detections.

Differential execution in this case just means that Dobby can run the same setup with multiple different engines, and report to the researcher where two engines have different execution paths or memory use. Combining this with reverse taint analysis allows us to narrow down a set of reasons why one engine acts different from another.

Symbolic Execution (actually "concolic" execution) allows us to denote areas of memory or registers as symbolic variables. Dobby will alert us when these variables are used as memory addresses, or used to decide which path execution will take. This allows us to denote much of our environment as symbolic and not worry about setting it up correctly until we see that the target binary even cares about it. It also allows us to do things like backward slicing to produce equations that tell us exactly how our variables were used to produce a value.

Many existing deobfuscation methods use some kind of lifting and optimization steps to try and produce equivalent code that is simpler. For a significantly complicated binary though, gathering the symbolic equations can explode in terms of memory and processing time. Dobby instead is not designed to be "fire and forget". Dobby works with the reverse engineer allowing symbolic expressions to be concretized into real values before the expressions grow too big for the machine to handle.

How does this tool compare to other projects?

This project is similar to a few other projects. For most use cases, you probably want a more mature tool. Below is a table comparing a few of them with Dobby.

Qiling Framework

Fireeye's Speakeasy

Panda

QEMU

Triton

Unicorn

Example

See the file beepexample.py

Installation Notes

This project depends on the following python3 packages, which can be installed with pip:

• triton
• pyvex
• lief
• unicorn