Emulate and Dissect MSF and *other* attacks

Overview

Logo

REW-sploit

The tool has been presented at Black-Hat Arsenal USA 2021

https://www.blackhat.com/us-21/arsenal/schedule/index.html#rew-sploit-dissecting-metasploit-attacks-24086

Slides of presentation are available at https://github.com/REW-sploit/REW-sploit_docs


Need help in analyzing Windows shellcode or attack coming from Metasploit Framework or Cobalt Strike (or may be also other malicious or obfuscated code)? Do you need to automate tasks with simple scripting? Do you want help to decrypt MSF generated traffic by extracting keys from payloads?

REW-sploit is here to help Blue Teams!

Here a quick demo:

asciicast

Install

Installation is very easy. I strongly suggest to create a specific Python Env for it:

# python -m venv /rew-sploit
# source /bin/activate
# git clone https://github.com/REW-sploit/REW-sploit.git
# cd REW-sploit
# pip install -r requirements.txt
# ./apply_patch.py -f
# ./rew-sploit

If you prefer, you can use the Dockerfile. To create the image:

docker build -t rew-sploit/rew-sploit .

and then start it (sharing the /tmp/ folder):

docker run --rm -it --name rew-sploit -v /tmp:/tmp rew-sploit/rew-sploit

You see an apply_patch.py script in the installation sequence. This is required to apply a small patch to the speakeasy-emulator (https://github.com/fireeye/speakeasy/) to make it compatible with REW-sploit. You can easily revert the patch with ./apply_patch.py -r if required.

Optionally, you can also install Cobalt-Strike Parser:

# cd REW-sploit/extras
# git clone https://github.com/Sentinel-One/CobaltStrikeParser.git

Standing on the shoulder of giants

REW-sploit is based on a couple of great frameworks, Unicorn and speakeasy-emulator (but also other libraries). Thanks to everyone and thanks to the OSS movement!

How it works

In general we can say that whilst Red Teams have a lot of tools helping them in "automating" attacks, Blue Teams are a bit "tool-less". So, what I thought is to build something to help Blue Team Analysis.

REW-sploit can get a shellcode/DLL/EXE, emulate the execution, and give you a set of information to help you in understanding what is going on. Example of extracted information are:

You can find several examples on the current capabilities here below:

Fixups

In some cases emulation was simply breaking, for different reasons. In some cases obfuscation was using some techniques that was confusing the emulation engine. So I implemented some ad-hoc fixups (you can enable them by using -F option of the emulate_payload command). Fixups are implemented in modules/emulate_fixups.py. Currently we have

Unicorn issue #1092:

    #
    # Fixup #1
    # Unicorn issue #1092 (XOR instruction executed twice)
    # https://github.com/unicorn-engine/unicorn/issues/1092
    #               #820 (Incorrect memory view after running self-modifying code)
    # https://github.com/unicorn-engine/unicorn/issues/820
    # Issue: self modfying code in the same Translated Block (16 bytes?)
    # Yes, I know...this is a huge kludge... :-/
    #

FPU emulation issue:

    #
    # Fixup #2
    # The "fpu" related instructions (FPU/FNSTENV), used to recover EIP, sometimes
    # returns the wrong addresses.
    # In this case, I need to track the first FPU instruction and then place
    # its address in STACK when FNSTENV is called
    #

Trap Flag evasion:

    #
    # Fixup #3
    # Trap Flag evasion technique
    # https://unit42.paloaltonetworks.com/single-bit-trap-flag-intel-cpu/
    #
    # The call of the RDTSC with the trap flag enabled, cause an unhandled
    # interrupt. Example code:
    #        pushf
    #        or dword [esp], 0x100
    #        popf
    #        rdtsc
    #
    # Any call to RDTSC with Trap Flag set will be intercepted and TF will
    # be cleared
    #

Customize YARA rules

File modules/emulate_rules.py contains the YARA rules used to intercept the interesting part of the code, in order to implement instrumentation. I tried to comment as much as possible these sections in order to let you create your own rule (please share them with a pull request if you think they can help others). For example:

#
# Payload Name: [MSF] windows/meterpreter/reverse_tcp_rc4
# Search for  : mov esi,dword ptr [esi]
#               xor esi,0x
# Used for    : this xor instruction contains the constant used to
#               encrypt the lenght of the payload that will be sent as 2nd
#               stage
# Architecture: x32
#
yara_reverse_tcp_rc4_xor_32 = 'rule reverse_tcp_rc4_xor {                \
                               strings:                                  \
                                   $opcodes_1 = { 8b 36                  \
                                                  81 f6 ?? ?? ?? ?? }    \
                               condition:                                \
                                   $opcodes_1 }'

Issues

Please, open Issues if you find something that not work or that can be improved. Thanks!

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Comments
  • shellcode:  Caught error: 'NoneType' object has no attribute 'startswith'

    shellcode: Caught error: 'NoneType' object has no attribute 'startswith'

    command: (REW-sploit)<<emulate_payload -P shell.bin -U 0

    0x10d3: Error while calling API handler for kernel32.VirtualAllocEx: Traceback: File ".../speakeasy/windows/winemu.py", line 1168, in handle_import_func rv = self.api.call-api_func(mod, func, argv, ctx=default_ctx) File ".../speakeasy/winenv/api/winapi.py", line 77, in call_api_func return func(mod, self.emu, argv, ctx) File ".../speakeasy/winenv/api/usermode/kernel32.py" line 995, in VirtualAllocEx if mm and mm.get_tag().startswith(tag_prefix): AttributeError: 'NoneType' object has no attribute 'startswith' 0x77...: shellcode: Caught error: 'NoneType' object has no attribute 'startswith'

    • Timeout of 0 sec(s) reached.
    • [+] Emulation ended
    opened by programmer4python 37
  • Antidebug detection feature

    Antidebug detection feature

    This will be released in version 0.4.0:

    • a new emulation option will execute the provided DLL/EXE/Shellcode to identify location of anti-debug techniques
    enhancement 
    opened by cecio 3
  • Reduced container image size

    Reduced container image size

    Modified Dockerfile to reduce the image size:

    $ docker image ls rew-sploit
    REPOSITORY   TAG       IMAGE ID       CREATED         SIZE
    rew-sploit   devel     e6e5b0244a0f   8 minutes ago   209MB
    rew-sploit   latest    1c477a013cc2   9 days ago      1.1GB
    
    opened by camandel 3
  • Not working with MSF payload x64

    Not working with MSF payload x64

    Hey,

    Here is what I tried to test your tool, first I generate a classic reverse TCP:

    msfvenom -p windows/x64/shell/reverse_tcp LHOST=127.0.0.1 LPORT=4444 -o test.bin -f raw
    

    Then I tried to emulate it with REW-sploit:

    (REW-sploit)<< emulate_payload -P samples/test.bin
    

    But here is the output:

    [+] Starting emulation
    * exec: shellcode
    0x10fb: shellcode: Caught error: invalid_write
    * Timeout of 0 sec(s) reached.
    [+] Emulation ended
    

    I also tried with this shellcode:

    msfvenom -p windows/x64/messagebox TITLE='Title' TEXT='Text' EXITFUNC=thread -f raw -o msgbox.bin
    

    However, examples in the samples folder are working fine (e.g: payload_tcp_rc4.bin), do you have an idea of what I'm doing wrong ?

    opened by lap1nou 2
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