Cyber Security in today’s world has become more challenging than
traditional days where we had Firewall and antivirus as our main defense
systems. Modern day adversary have got all the necessary resources – (Time,
Team & Money) to execute their tasks of getting a victim compromised. Most
of the offensive techniques tools such as Metasploit, Empire could get easily
detected by Next-generation Antivirus or IDS/IPS running within the
infrastructure of organization. In order to bypass the Cyber security defense,
an adversary may write custom code using programming languages.
This article post is based on “Windows API Exploitation Recipes” course from
Pentester Academy.
Exploiting victim using custom code would be golden game for an adversary as
most of the signature based defense solutions would not be able to detect the
attack. We would be utilising Windows built in APIs to look at some specific
techniques which could ensure stealth and undetectability for adversary for as
long time as possible. We would be mostly focusing on post exploitation phase
of attacker life cycle. Below are few of the pre-requisites which would be
required for us to perform this API exploitation techniques –

  • Programming language – C
  • Windows 10
  • Visual Studio 2022

As mentioned earlier, powerful adversaries typically develop custom code to
ensure stealthier persistence. We have divided this topic of API exploitation in
multiple different sections. In this section, we will specifically look at Process
Listing APIs using Windows.
Process listing could be very interesting in real world scenario, which helps as
an adversary –

  • To understand/enumerate which all processes are running on victim
  • Identify any antivirus, IDS, IPS running on system
  • Starting point for process level attacks such as process injection,
    Memory dump, etc.

There are multiple ways which can be used to perform process listing using
Windows APIs.

  1. WTSEnumerateProcessesEx
  2. CreateToolhelp32Snapshot
  3. PSAPI Enumprocess

Let’s consider an example for process listing – PSAPI Enumprocess
Retrieves the process identifier for each process object in the system.

Enumprocesses will give us the list of process IDs. In order to get more
information for particular process, we need to call OpenProcess() API after

We need to consider that few of the API functions and methods will fail in the
if we don’t have privilege session, in such cases we need to enable
SeDebugPrivilege on current process token. This would be considered in our
code walk through-

Enumprocesses() – this function as seen in code snippet is going to fill in all the
pids currently in the system and will provide the output to us.
Next step involves actually applying OpenProcess() API in order to get
processhandle and once we get process handle to any particular process — >
GetProcessImageFileName() is called in order to get entire path of the exe
which is currently running on system.

This code needs to be compiled using Microsoft visual studio and once we
compile the code, we need to run the output exe file using command prompt.
There would be an interesting observation once we run the code using normal
user cmd prompt. Our code would be able to provide us results in most of the
cases but there would be few entries where “Error: Access is denied” is
Reason being we don’t have enough privileges to get more interesting
information, running the code using Administrative command prompt will help
us to get results similar to what we would observe using tool like process

As simple as that!
This is how modern day threat actors develop custom code toolsets which can
be used to perform multiple operations and which could get undetected by
most of our prevention/detection security solutions.
As an example, we have discussed about process listing APIs but in reality we
can have many of such use cases – Process token dumping, Read process
memory, writing to process memory using set of Windows APIs and by
developing custom code template to perform particular operations.
This would require some basic knowledge of programming but the application
of exploiting the knowledgebase of Windows APIs would be huge. And by
understanding the approach of how modern day threat adversary would
definitely help blue teamers to improve their defense mechanism and stay a
step ahead of an attacker.