Invoke-Obfuscation v1.8
Introduction
Invoke-Obfuscation is a PowerShell v2.0+ compatible PowerShell command
and script obfuscator.
Background
In the Fall of 2015 I decided to begin researching the flexibility of
PowerShell's language and began cataloguing the various ways to
accomplish a handful of common techniques that most attackers use on a
regular basis.
Initially focusing on encoded command and remote download cradle syntaxes,
I discovered that various escape characters that did not hinder the
execution of the command persisted in the command line arguments, both in
the running process as well as what is logged in Security EID 4688 and
Sysmon EID 1 event logs. This led me to systematically explore ways of
obfuscating each kind of "token" found in any PowerShell command or script.
I then explored more obscure ways to perform string-level obfuscation,
various encoding/encrypting techniques (like ASCII/hex/octal/binary and even
SecureString), and finally PowerShell launch techniques to abstract the
command line arguments from powershell.exe and to push it back to the parent
and even grandparent process.
Purpose
Attackers and commodity malware have started using extremely basic
obfuscation techniques to hide the majority of the command from the command
line arguments of powershell.exe. I developed this tool to aid the Blue Team
in simulating obfuscated commands based on what I currently know to be
syntactically possible in PowerShell 2.0-5.0 so that they can test their
detection capabilities of these techniques.
The tool's sole purpose is to break any assumptions that we as defenders may
have concerning how PowerShell commands can appear on the command line. My
hope is that it will encourage the Blue Team to shift to looking for
Indicators of Obfuscation on the command line in addition to updating
PowerShell logging to include Module, ScriptBlock and Transcription logging
as these sources simplify most aspects of the obfuscation techniques
generated by this tool.
Usage
While all of the layers of obfuscation have been built out into separate
scripts, most users will find the Invoke-Obfuscation function to be the
easiest way to explorer and visualize the obfuscation techniques that this
framework currently supports.
Installation
The source code for Invoke-Obfuscation is hosted at Github, and you may
download, fork and review it from this repository
(https://github.com/danielbohannon/Invoke-Obfuscation). Please report issues
or feature requests through Github's bug tracker associated with this project.
To install:
Import-Module ./Invoke-Obfuscation.psd1
Invoke-Obfuscation
License
Invoke-Obfuscation is released under the Apache 2.0 license.
Release Notes
v1.0 - 2016-09-25 DerbyCon 6.0 (Louisville, Kentucky USA): PUBLIC Release of Invoke-Obfuscation.
v1.1 - 2016-10-09 SANS DFIR Summit (Prague, Czech Republic): Added -f format operator re-ordering
functionality to all applicable TOKEN obfuscation functions. Also added additional
syntax options for setting variable values.
v1.2 - 2016-10-20 CODE BLUE (Tokyo, Japan): Added Type TOKEN obfuscation (direct type
casting with string obfuscation options for type name).
v1.3 - 2016-10-22 Hacktivity (Budapest, Hungary): Added two new LAUNCHERs: CLIP+ and CLIP++.
Also added additional (and simpler) array char conversion syntax for all ENCODING
functions that does not require For-EachObject/%.
v1.4 - 2016-10-28 BruCON (Ghent, Belgium): Added new BXOR ENCODING function. Also enhanced
randomized case for all components of all ENCODING functions as well as for
PowerShell execution flags for all LAUNCHERs. Finally, added -EP shorthand option
for -ExecutionPolicy to all LAUNCHERs as well as the optional integer representation
of the -WindowStyle PowerShell execution flag: Normal (0), Hidden (1), Minimized (2),
Maximized (3).
v1.5 - 2016-11-04 Blue Hat (Redmond, Washington USA): Added WMIC LAUNCHER with some
randomization of WMIC command line arguments.
v1.6 - 2017-01-24 Blue Hat IL (Tel Aviv, Israel):
- Added CLI functionality:
E.g., Invoke-Obfuscation -ScriptBlock {Write-Host 'CLI FTW!'} -Command 'Token\All\1,
Encoding\1,Launcher\Stdin++\234,Clip' -Quiet -NoExit
- Added UNDO functionality to remove one layer of obfuscation at a time.
- Removed Whitespace obfuscation from Token\All\1 to speed up large script obfuscation.
- Added Process Argument Tree output for all launchers to aid defenders.
- Added base menu auto-detect functionality to avoid needing to use BACK or HOME:
E.g., if you ran TOKEN then ALL then 1, then just type LAUNCHER and you will get to
the LAUNCHER menu without needing to type HOME or BACK to get back to the home menu.
- Added multi-command syntax utilized by CLI and interactive mode:
E.g., Token\All\1,String\3,Encoding\5,Launcher\Ps\234,Clip
- Added regex capability to all menu and obfuscation commands:
E.g., Token**,String[13],Encoding(1|6),Launcher.*[+]{2}\234,Clip
- Added OUT FILEPATH single command functionality.
- Added decoding if powershell -enc syntax is entered as a SCRIPTBLOCK value.
- Added alias ForEach to ForEach-Object/% randomized syntax options in all ENCODING
functions.
- Added -Key -Ke -K KEY substring syntax options to Out-SecureStringCommand.ps1.
- Added more thorough case randomization to all \Home\String obfuscation functions.
- Added -ST/-STA (Single-Threaded Apartment) flags to CLIP+ and CLIP++ launcher
functions since they are required if running on PowerShell 2.0.
- Added Get-Item/GI/Item syntax everywhere where Get-ChildItem is used to get
variable values.
- Added Set-Item variable instantiation syntax to TYPE obfuscation function.
- Added additional Invoke-Expression/IEX syntax using PowerShell automatic variables
and environment variable value concatenations in Out-ObfuscatedStringCommand.ps1's
Out-EncapsulatedInvokeExpression function and copied to all launchers, STRING and
ENCODING functions to add numerous command-line syntaxes for IEX.
- Added two new JOIN syntaxes for String\Reverse and all ENCODING obfuscation options:
- Added [String]::Join('',$string) JOIN syntax
- Added OFS-variable JOIN syntax (Output Field Separator automatic variable)
- Added two more SecureString syntaxes to Encoding\5:
- PtrToStringAnsi / SecureStringToGlobalAllocAnsi
- PtrToStringBSTR / SecureStringToBSTR
- Added six GetMember alternate syntaxes for several SecureString members:
- PtrToStringAuto, ([Runtime.InteropServices.Marshal].GetMembers()[3].Name).Invoke
- PtrToStringAuto, ([Runtime.InteropServices.Marshal].GetMembers()[5].Name).Invoke
- PtrToStringUni , ([Runtime.InteropServices.Marshal].GetMembers()[2].Name).Invoke
- PtrToStringUni , ([Runtime.InteropServices.Marshal].GetMembers()[4].Name).Invoke
- PtrToStringAnsi, ([Runtime.InteropServices.Marshal].GetMembers()[0].Name).Invoke
- PtrToStringAnsi, ([Runtime.InteropServices.Marshal].GetMembers()[1].Name).Invoke
- Updated Out-ObfuscatedTokenCommand.ps1 so that VARIABLE obfuscation won't
encapsulate variables in ${} if they are already encapsulated (so ${${var}} won't
happen as this causes errors).
- Replaced Invoke-Obfuscation.psm1 with Invoke-Obfuscation.psd1 (thanks @Carlos_Perez).
- Fixed several TOKEN-level obfuscation bugs reported by @cobbr_io and @IISResetMe.
v1.7 - 2017-03-03 nullcon (Goa, India):
- Added 3 new LAUNCHERs: RUNDLL, RUNDLL++ and MSHTA++
- Added additional ExecutionContext wildcard variable strings
v1.8 - 2017-07-27 Black Hat (Las Vegas, Nevada USA):
- Added 2 new ENCODING options: Special Characters and Whitespace
v1.8.1 - 2017-12-19:
- Added COMPRESS function for easier conversion of multi-line scripts to a one-liner
command while drastically reducing the command length for cmd.exe command line length
limitation purposes.
v1.8.2 - 2018-01-04:
- Added AST obfuscation functions, which obfuscates by manipulating the structure of
the AbstractSyntaxTree without using many special characters.
