Avast Open Sources Machine-Code Decompiler in Battle Against Malware

In an effort to boost the fight against malicious software, anti-malware company Avast this week announced the release of its retargetable machine-code decompiler as open source.

Dubbed RetDec, short for Retargetable Decompiler, the software utility is the result of seven years of development and was originally created as a joint project by the Faculty of Information Technology of the Brno University of Technology in the Czech Republic, and AVG Technologies. Avast acquired AVG Technologies in 2016.

The tool allows the security community to perform platform-independent analysis of executable files. With its source code published to GitHub under the MIT license, RetDec is now available for anyone to freely use it, study its source code, modify it, and redistribute it.

By open-sourcing the decompiler, Avast aims to provide “a generic tool to transform platform-specific code, such as x86/PE executable files, into a higher form of representation, such as C source code.”

The analytical utility includes support for multiple platforms, different architectures, file formats, and compilers. It supports architectures such as: (32b only) Intel x86, ARM, MIPS, PIC32, and PowerPC, and the following file formats: ELF, PE, Mach-O, COFF, AR (archive), Intel HEX, and raw machine code.

Currently, the tool can be used on Windows and Linux machines, but pre-built packages are available for Windows only (Linux users need to build and install the decompiler by themselves).

RetDec can be used to perform static analysis of executable files with detailed information; for compiler and packer detection; for loading and instruction decoding; signature-based removal of statically linked library code; extraction and utilization of debugging information (DWARF, PDB), reconstruction of instruction idioms; detection and reconstruction of C++ class hierarchies (RTTI, vtables); demangling of symbols from C++ binaries (GCC, MSVC, Borland); reconstruction of functions, types, and high-level constructs; and generation of call graphs, control-flow graphs, and various statistics.

There is also an integrated disassembler to take advantage of and output is available in two languages: C and a Python-like language. Courtesy of an IDA plugin, decompilation of files directly from the IDA disassembler is also possible.

Decompilers aren’t normally able to perfectly reconstruct original source code because information is lost during the compilation process and because of the obfuscation techniques malware authors often use. According to Avast, RetDec addresses these issues “by using a large set of supported architectures and file formats, as well as in-house heuristics and algorithms to decode and reconstruct applications.”

In addition to publishing RetDec’s source code, Avast provides several ways to take full advantage of the decompiler, starting with its web service. The security company also made its IDA plugin available, along with an REST API that allows the creation of apps that can interact with RetDec through HTTP requests. The decompiler can be used via the API through retdec-python.

Ionut Arghire is an international correspondent for SecurityWeek.

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