Malware Persistence Mechanisms on Windows

In cybersecurity, understanding how malware maintains persistence in Windows environments is crucial for developing effective defense strategies.

Malware persistence mechanisms ensure that malicious software remains active on a system even after reboots, user logouts, or other interruptions.

These techniques can range from relatively simple registry modifications to sophisticated manipulation of system components.

The following discusses the various techniques and gives PowerShell script snippets to check for each type where appropriate. Note, these need to be executed in a PowerShell terminal.

Registry Modifications

The Windows Registry is a critical hierarchical database that stores low-level settings for the operating system and applications. Malware often exploits the registry to achieve persistence.

• Run Keys: Malware can add entries to the HKCU\Software\Microsoft\Windows\CurrentVersion\Run or HKLM\Software\Microsoft\Windows\CurrentVersion\Run keys. This ensures that the malware executes every time the user logs in.

Get-ItemProperty -Path 'HKCU:\Software\Microsoft\Windows\CurrentVersion\Run'
Get-ItemProperty -Path 'HKLM:\Software\Microsoft\Windows\CurrentVersion\Run'

• Services: By creating or modifying Windows services, malware can start automatically at boot. The CreateService and StartService functions in the Windows API facilitate this.

Get-Service | Where-Object { $_.PathName -like "malware" }

Scheduled Tasks

Malware can use the Windows Task Scheduler to create tasks that run at specific times or system events. This is done through the schtasks command or Task Scheduler API.

• Creating Tasks: A task can be scheduled to execute the malware at system startup or user logon.

schtasks /create /tn "MaliciousTask" /tr "malware.exe" /sc onlogon

• Listing Tasks: Reviewing scheduled tasks can help identify malicious entries.

Get-ScheduledTask | Where-Object { $_.TaskName -like "malware" }

DLL Injection

Dynamic-Link Library (DLL) injection is a technique where malware inserts malicious code into the address space of another process, enabling it to run with the privileges of that process.

• AppInit_DLLs: The AppInit_DLLs registry value can specify DLLs to be loaded into every process that uses User32.dll.

Get-ItemProperty -Path 'HKLM:\Software\Microsoft\Windows NT\CurrentVersion\Windows' -Name 'AppInit_DLLs'

• Reflective DLL Injection: This advanced technique involves loading a DLL directly into memory without using the Windows loader, making it harder to detect.

WMI Persistence

Windows Management Instrumentation (WMI) provides a powerful way to manage systems and automate administrative tasks. Malware can leverage WMI for persistence by creating permanent event subscriptions.

• WMI Event Subscription: Creating a WMI event filter and consumer to trigger malicious scripts or executables.

Get-WmiObject -Namespace root\subscription -Class __EventFilter

Bootkits and Rootkits

Bootkits and rootkits modify the boot process or core operating system components to gain persistence at a very low level.

• Bootkits: Infect the Master Boot Record (MBR) or Volume Boot Record (VBR), ensuring the malware loads before the operating system.

bootrec /fixmbr

Rootkits: Hide the presence of malware by intercepting and modifying OS operations. Tools like GMER can help detect rootkits.

PowerShell and Scripting

PowerShell is a powerful scripting language and shell framework that can be exploited for persistence.

• Profile Scripts: Malware can add malicious commands to PowerShell profile scripts (profile.ps1), which execute every time PowerShell starts.

Get-Content $PROFILE

• Scheduled Tasks with PowerShell: Combining PowerShell with scheduled tasks for stealthy persistence.

schtasks /create /tn "MaliciousPS" /tr "powershell -ExecutionPolicy Bypass -File C:\malware.ps1" /sc onlogon

Advanced Techniques

Sophisticated malware uses more advanced techniques to avoid detection and ensure persistence.

• Process Hollowing: Injecting malicious code into a legitimate process, replacing the legitimate code. This involves using the CreateProcess and WriteProcessMemory functions.
• Code Cave Injection: Injecting code into unused spaces within a legitimate executable, allowing malware to run as part of a trusted process.
• COM Hijacking: Modifying COM object registrations in the registry to redirect legitimate COM calls to malicious code.

Get-ItemProperty -Path 'HKCU:\Software\Classes\CLSID' -Recurse

Detection and Mitigation

To detect and mitigate malware persistence mechanisms, a combination of manual inspection and automated tools is essential.

• Autoruns: Sysinternals’ Autoruns utility can be used to identify and disable autostart programs, services, and other persistence mechanisms.

.\Autoruns64.exe

• Event Logs: Windows Event Logs can provide valuable information about suspicious activities related to persistence.

Get-WinEvent -LogName System | Where-Object { $_.Message -like "malware" }

• Behavioral Analysis: Using tools like Sysmon to log and analyze system behavior can help detect anomalies indicative of malware.

sysmon -accepteula -i sysmonconfig.xml

Summary

Understanding these malware persistence mechanisms and employing appropriate detection and mitigation strategies can significantly enhance the security posture of Windows systems. Regularly updating and patching systems, coupled with vigilant monitoring and analysis, can help protect against persistent malware threats.