Decompile compiled python binaries (exe, elf) - Retreive from .pyc - HackTricks

# Decompile compiled python binaries (exe, elf) - Retreive from .pyc

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## From Compiled Binary to .pyc

From an ELF compiled binary you can get the .pyc with:

    pyi-archive_viewer <binary>
    # The list of python modules will be given here:
    [(0, 230, 311, 1, 'm', 'struct'),
     (230, 1061, 1792, 1, 'm', 'pyimod01_os_path'),
     (1291, 4071, 8907, 1, 'm', 'pyimod02_archive'),
     (5362, 5609, 13152, 1, 'm', 'pyimod03_importers'),
     (10971, 1473, 3468, 1, 'm', 'pyimod04_ctypes'),
     (12444, 816, 1372, 1, 's', 'pyiboot01_bootstrap'),
     (13260, 696, 1053, 1, 's', 'pyi_rth_pkgutil'),
     (13956, 1134, 2075, 1, 's', 'pyi_rth_multiprocessing'),
     (15090, 445, 672, 1, 's', 'pyi_rth_inspect'),
     (15535, 2514, 4421, 1, 's', 'binary_name'),
    ...

    ? X binary_name
    to filename? /tmp/binary.pyc

In a python exe binary compiled you can get the .pyc by running:

    python pyinstxtractor.py executable.exe

## From .pyc to python code

For the .pyc data ("compiled" python) you should start trying to extract the original python code:

    uncompyle6 binary.pyc  > decompiled.py

Be sure that the binary has the extension ".pyc" (if not, uncompyle6 is not going to work)

While executing uncompyle6 you might find the following errors:

### Error: Unknown magic number 227

    /kali/.local/bin/uncompyle6 /tmp/binary.pyc
    Unknown magic number 227 in /tmp/binary.pyc

To fix this you need to add the correct magic number at the beginning of the generated file.

Magic numbers vary with the python version, to get the magic number of python 3.8 you will need to open a python 3.8 terminal and execute:

    >> import imp
    >> imp.get_magic().hex()
    '550d0d0a'

The magic number in this case for python3.8 is `0x550d0d0a`, then, to fix this error you will need to add at the beginning of the .pyc file the following bytes: `0x0d550a0d000000000000000000000000`

Once you have added that magic header, the error should be fixed.

This is how a correctly added .pyc python3.8 magic header will look like:

    hexdump 'binary.pyc' | head
    0000000 0d55 0a0d 0000 0000 0000 0000 0000 0000
    0000010 00e3 0000 0000 0000 0000 0000 0000 0000
    0000020 0700 0000 4000 0000 7300 0132 0000 0064
    0000030 0164 006c 005a 0064 0164 016c 015a 0064

### Error: Decompiling generic errors

Other errors like: `class 'AssertionError'>; co_code should be one of the types (<class 'str'>, <class 'bytes'>, <class 'list'>, <class 'tuple'>); is type <class 'NoneType'>` may appear.

This probably means that you haven't added correctly the magic number or that you haven't used the correct magic number, so make sure you use the correct one (or try a new one).

Check the previous error documentation.

## Automatic Tool

The python-exe-unpacker tool serves as a combination of several community-available tools designed to assist researchers in unpacking and decompiling executables written in Python, specifically those created with py2exe and pyinstaller. It includes YARA rules to identify if an executable is Python-based and confirms the creation tool.

### ImportError: File name: 'unpacked/malware_3.exe/pycache/archive.cpython-35.pyc' doesn't exist

A common issue encountered involves an incomplete Python bytecode file resulting from the unpacking process with unpy2exe or pyinstxtractor, which then fails to be recognized by uncompyle6 due to a missing Python bytecode version number. To address this, a prepend option has been added, which appends the necessary Python bytecode version number, facilitating the decompiling process.

Example of the issue:

    # Error when attempting to decompile without the prepend option
    test@test: uncompyle6 unpacked/malware_3.exe/archive.py
    Traceback (most recent call last):
    ...
    ImportError: File name: 'unpacked/malware_3.exe/__pycache__/archive.cpython-35.pyc' doesn't exist

    # Successful decompilation after using the prepend option
    test@test:python python_exe_unpack.py -p unpacked/malware_3.exe/archive
    [*] On Python 2.7
    [+] Magic bytes are already appended.

    # Successfully decompiled file
    [+] Successfully decompiled.

## Analyzing python assembly

If you weren't able to extract the python "original" code following the previous steps, then you can try to extract the assembly (but it isn't very descriptive, so try to extract again the original code).In here I found a very simple code to disassemble the .pyc binary (good luck understanding the code flow). If the .pyc is from python2, use python2:

    >>> import dis
    >>> import marshal
    >>> import struct
    >>> import imp
    >>>
    >>> with open('hello.pyc', 'r') as f:  # Read the binary file
    ...     magic = f.read(4)
    ...     timestamp = f.read(4)
    ...     code = f.read()
    ...
    >>>
    >>> # Unpack the structured content and un-marshal the code
    >>> magic = struct.unpack('<H', magic[:2])
    >>> timestamp = struct.unpack('<I', timestamp)
    >>> code = marshal.loads(code)
    >>> magic, timestamp, code
    ((62211,), (1425911959,), <code object <module> at 0x7fd54f90d5b0, file "hello.py", line 1>)
    >>>
    >>> # Verify if the magic number corresponds with the current python version
    >>> struct.unpack('<H', imp.get_magic()[:2]) == magic
    True
    >>>
    >>> # Disassemble the code object
    >>> dis.disassemble(code)
      1           0 LOAD_CONST               0 (<code object hello_world at 0x7f31b7240eb0, file "hello.py", line 1>)
                  3 MAKE_FUNCTION            0
                  6 STORE_NAME               0 (hello_world)
                  9 LOAD_CONST               1 (None)
                 12 RETURN_VALUE
    >>>
    >>> # Also disassemble that const being loaded (our function)
    >>> dis.disassemble(code.co_consts[0])
      2           0 LOAD_CONST               1 ('Hello  {0}')
                  3 LOAD_ATTR                0 (format)
                  6 LOAD_FAST                0 (name)
                  9 CALL_FUNCTION            1
                 12 PRINT_ITEM
                 13 PRINT_NEWLINE
                 14 LOAD_CONST               0 (None)
                 17 RETURN_VALUE

## Python to Executable

To start, we’re going to show you how payloads can be compiled in py2exe and PyInstaller.

### To create a payload using py2exe:

1. Install the py2exe package from http://www.py2exe.org/
2. For the payload (in this case, we will name it hello.py), use a script like the one in Figure 1. The option “bundle_files” with the value of 1 will bundle everything including the Python interpreter into one exe.
3. Once the script is ready, we will issue the command “python setup.py py2exe”. This will create the executable, just like in Figure 2.

    from distutils.core import setup
    import py2exe, sys, os

    sys.argv.append('py2exe')

    setup(
        options = {'py2exe': {'bundle_files': 1}},
        #windows = [{'script': "hello.py"}],
      console = [{'script': "hello.py"}],
        zipfile = None,
    )

    C:\Users\test\Desktop\test>python setup.py py2exe
    running py2exe
    *** searching for required modules ***
    *** parsing results ***
    *** finding dlls needed ***
    *** create binaries ***
    *** byte compile python files ***
    *** copy extensions ***
    *** copy dlls ***
    copying C:\Python27\lib\site-packages\py2exe\run.exe -> C:\Users\test\Desktop\test\dist\hello.exe
    Adding python27.dll as resource to C:\Users\test\Desktop\test\dist\hello.exe

### To create a payload using PyInstaller:

1. Install PyInstaller using pip (pip install pyinstaller).
2. After that, we will issue the command “pyinstaller –onefile hello.py” (a reminder that ‘hello.py’ is our payload). This will bundle everything into one executable.

    C:\Users\test\Desktop\test>pyinstaller --onefile hello.py
    108 INFO: PyInstaller: 3.3.1
    108 INFO: Python: 2.7.14
    108 INFO: Platform: Windows-10-10.0.16299
    ………………………………
    5967 INFO: checking EXE
    5967 INFO: Building EXE because out00-EXE.toc is non existent
    5982 INFO: Building EXE from out00-EXE.toc
    5982 INFO: Appending archive to EXE C:\Users\test\Desktop\test\dist\hello.exe
    6325 INFO: Building EXE from out00-EXE.toc completed successfully.

## References

- https://blog.f-secure.com/how-to-decompile-any-python-binary/

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