Anti Forensic: Overwriting executable while it is still running

Download from: https://github.com/jmprsp/ProcessFailures

Reference: https://recon.cx/2016/talks/Process-Failure-Modes.html

As presented in RECON 2016 by James Forshaw. He demonstrated that he is able to overwrite an application’s physical file while it is still running as a process. According to his presentation, NtCreateUserProcess returns a file handle when it is called. The file handle can be used to overwrite the running process His POC is in the form of C#/Powershell. I simply converted it to C/Executable.

slides
Figure 1. NtCreateUserProcess returning file handle

To demonstrate that it really work, I used an executable that simply popup a message box; named demo.pdf. You can see the hexadecimal of the binary file in the HxD GUI below. On executing Overwrite.exe, demo.pdf will be created as a process and while it is still running, Overwrite.exe will then overwrite demo.pdf with an actual pdf file (Process Failure modes – Final.pdf).

setup
Figure 2. Initial Setup

Usage of the program is as follows: Overwrite.exe [Full path to executable] [input file]

overwritten
Figure 3. demo.pdf overwritten with actual pdf

As we can see from the above screenshot, demo.pdf is executed as a process but HxD has already reflected the new bytes in Demo.pdf. We can also observe that demo.pdf file size has changed to 3MB from 165KB proving that this trick did indeed work.

From a RE point of view, we should keep a look out on the CREATE_INFO’s AdditionalFileAccess mask and the usage of undocumented API as shown below.

accessmask
Figure 4. AdditionalFileAccess Mask

 

Anti Forensic: Overwriting executable while it is still running

Executing DLL as a Process

Download from: https://github.com/jmprsp/ProcessFailures

Reference: https://recon.cx/2016/talks/Process-Failure-Modes.html

As presented in RECON 2016 by James Forshaw. He demonstrated that he is able to execute a DLL as a standalone process. According to his presentation, the reason why a DLL can’t be executed as a process is due to a check on the ProhibitedImageCharacteristics field. His POC is in the form of C#/Powershell. I simply converted it to C/Executable.

ProhibitedImageCharacteristics
Figure 1. ProhibitedImageCharacteristics

So by simply resetting this field to 0, we could then run a DLL as a process!

The following is a DLL with a .txt extension; just for fun… using regsvr32 is one of the way to execute a DLL and as you can see, a messagebox shows up stating that it is a DLL.

dll
Figure 2. running a DLL

Now using James approach, we can now execute pikachu.txt as an executable!

Executable
Figure 3. running the DLL as a process
taskmanager
Figure 4. pikachu.txt running as a process

Looking it from IDA Pro

Clear.PNG
Figure 5. Clearing ProhibitedImageCharacteristics

Note that one do not necessary need to clear the field with 0. Other values work as well.

Executing DLL as a Process

JmpRsp on github

Will be uploading some binaries @ https://github.com/jmprsp

The first project will be on Process Mode Failures by James Forshaw as presented in Recon 2016. The POC given by James is in Powershell/C#. I reproduced some of his work into C. Over the next few days you will find the following executables in github.

  1. Executing DLL as a process [Uploaded]
  2. Overwriting the physical file of a binary while it is still running as a process  [Uploaded]

Reference: https://recon.cx/2016/talks/Process-Failure-Modes.html

JmpRsp on github