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Obfuscated Files or Information: Steganography
![Defense Evasion [Mitre] icon](/media/2024/04/08/icons8-burglar.svg){kind=small}
Adversaries may use steganography techniques in order to prevent the detection of hidden information. Steganographic techniques can be used to hide data in digital media such as images, audio tracks, video clips, or text files.
Duqu was an early example of malware that used steganography. It encrypted the gathered information from a victim's system and hid it within an …
Read moreProcess Injection: Extra Window Memory Injection
Adversaries may inject malicious code into process via Extra Window Memory (EWM) in order to evade process-based defenses as well as possibly elevate privileges. EWM injection is a method of executing arbitrary code in the address space of a separate live process.
Before creating a window, graphical Windows-based processes must prescribe to or register a windows class, which stipulate …
Read moreSubvert Trust Controls: Mark-of-the-Web Bypass
Adversaries may abuse specific file formats to subvert Mark-of-the-Web (MOTW) controls. In Windows, when files are downloaded from the Internet, they are tagged with a hidden NTFS Alternate Data Stream (ADS) named Zone.Identifier with a specific value known as the MOTW. Files that are tagged with MOTW are protected and cannot perform certain actions. For example, starting in MS Office …
Read moreSystem Script Proxy Execution: PubPrn
Adversaries may use PubPrn to proxy execution of malicious remote files. PubPrn.vbs is a Visual Basic script that publishes a printer to Active Directory Domain Services. The script may be signed by Microsoft and is commonly executed through the Windows Command Shell via Cscript.exe. For example, the following code publishes a printer within the specified domain: cscript pubprn Printer1 LDAP://CN=Container1,DC=Domain1,DC=Com.
… Read moreCall to Interrupt Procedure
This anti-debugging technique involves using the INT n instruction to generate a call to the interrupt or exception handler specified with the destination operand.
To implement this technique, the int 0x03 instruction is executed, followed by a ret (0xCD03, 0xC3) nested in a __try, __except block. If a debugger is present, the except block will not be executed, …
Unloading Module with FreeLibrary
Malware authors often use various techniques to evade detection by AV/EDR solutions. One such technique involves checking for the presence of AV/EDR DLLs that may be loaded in the malware's address space and attempting to unload them before executing their malicious code.
To do this, the malware first uses the GetModuleHandleA function to retrieve a handle to the DLL, …
Evasion using direct Syscalls
In the Windows operating system, conventional malware frequently utilizes strategies involving the invocation of specific functions from the kernel32.dll library, such as VirtualAlloc, VirtualProtect, and CreateThread. A closer inspection of the call stack reveals that the functions employed from kernel32.dll eventually trigger corresponding functions within the ntdll.dll library. This is facilitated by the ntdll.dll library, which serves …
Process Argument Spoofing
Process Argument Spoofing is a technique used by attackers to hide their true intentions by changing the command line arguments of a process after it has started.
--windows-- This is done by tampering with the Process Environment Block (PEB).
The PEB is a structure in Windows that holds various information about a running process. Within the PEB, there's …
Read moreBlockInput
As per Microsoft's documentation, BlockInput function "prevents keyboard and mouse input events from reaching applications," effectively restricting user interaction with the system.
Malware occasionally employs this tactic to hinder analysis by debuggers or other analysis tools throughout the process' runtime. To deactivate the block, the program must make a live call to BlockInput with the parameter 0. Windows automatically …
VBA Purging
VBA Purging is an obfuscation technique designed to evade detection mechanisms used in malware analysis. When a VBA macro is added to a Microsoft Office document, it is stored in two sections: the PerformanceCache (compiled VBA code) and the CompressedSourceCode (compressed VBA source code). In VBA Purging, the PerformanceCache (compiled code) is completely removed from the module stream, along with …
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