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README.md

Bitdefender Shellocde Emulator Fuzzer

This assumes that you have AFL in your path.

It collects the bddisasm and bdshemu sources into a single executable, built with AFL instrumentation.

Getting started

Build it with make shfuzz.

Start fuzzing with make fuzz32 (for 32-bit mode samples) or make fuzz64 (for 64-bit mode samples).

If you're in a hurry you can fuzz in the quick and dirty mode with DIRTY=y: make fuzz32 DIRTY=y or make fuzz64 DIRTY=y.

Activate support for address sanitizer with AFL_USE_ASAN=1 make shfuzz. This can uncover more bugs, but it is a lot slower and requires more memory.

Input files are in the in-32 and in-64 directories, crashes will be in out-32/crashes or out-64/crashes, hangs will be in out-32/hangs or out-64/hangs.

Details

If the AFL_COMPILER variable is not set, the build process looks for afl-clang-fast and if it is available, the tool is compiled with that. If not, it tries to choose between afl-clang and afl-gcc. If you want to use a certain compiler simply set AFL_COMPILER before invoking make: AFL_COMPILER=afl-gcc make. Note that afl-clang-fast is not compiled by default when compiling AFL. See llvm mode in the AFL repository.

Run the fuzzer in 32-bit mode with make fuzz32, or in 64-bit mode with make fuzz64.

If you want to take advantage of multiple cores see parallel fuzzing.

If afl-clang-fast is used, we try to use AFL in persistent mode, which should provide better performance.

Note that both fuzz32 and fuzz64 assume that the tool was compiled with afl-clang-fast, afl-clang, or afl-gcc.

ASAN builds will have increased memory requirements. You may need to tweak the -m parameter (or set AFL_MEMORY) for afl-fuzz (see notes for ASAN).

By default, all logging is disabled, as it is already not visible while AFL is running. Compile with LOG=y in order to enable some minimal logging.

Using the tool

The shfuzz tool is a simplified version of disasmtool. It takes 3 positional arguments:

shfuzz file mode use_logging
  • file - the path to a input file that contains instructions to be disassembled and emulated;
  • mode - the mode in which to run: 32 for 32-bit instructions, 64 for 64-bit instruction;
  • use_logging - if present, will actually log everything that bdshemu wants to log; even if absent, the ShemuLog implementation will still try to access every character in the string it should normally print, so if you want to find bugs related to logging you can still do, but it is a lot faster when the strings don't get printed. This is ignored if you compile shfuzz without LOG=y.

Any errors encountered while parsing the arguments, trying to open the input file, or allocate memory are handled by calling abort(). This makes it easier to detect these problems.