T1547.003 Time Providers is a technique in the MITRE ATT&CK framework under the Persistence tactic. It involves the W32Time service in Windows, which ensures time synchronization within and across domains.
Time providers, implemented as Dynamic Link Libraries (DLLs), are responsible for fetching and distributing time stamps from various sources to keep system clocks synchronized. These time providers are registered in the Windows Registry, making them integral to the system’s time management. The time provider mechanism is critical for proper time synchronization and is used to align logs, authentication events, and other system activities across networked machines.
To read about other sub-techniques of the T1547 Boot Logon or Auto Start Execution technique, you can visit the related hub blog.
Adversaries aiming to maintain persistence on a Windows system may target the W32Time service, a critical component for time synchronization in network operations. They achieve this by manipulating a specific registry key:
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HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\W32Time\TimeProviders\ |
By obtaining administrative privileges, attackers can alter this registry key to include a malicious DLL. This is typically done using the reg add command. For instance, they might add a new subkey to register their malicious DLL as a time provider, using a command like:
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"HKLM\System\CurrentControlSet\Services\W32Time\TimeProviders\MyMaliciousTimeProvider" /v "DllName" /d "C:\Path\To\Malicious.dll" /f |
This method is covert and effective, embedding the malware within an essential system service. When the system boots up or the W32Time service is restarted, the service control manager loads the registered time providers, including the malicious DLL. This DLL, running under the Local Service account, possesses sufficient privileges to carry out various malicious activities, exploiting the critical role of the time synchronization service in network operations.
To mitigate the risk of adversaries exploiting the W32Time service in Windows systems, a combination of restrictive measures is essential. Implementing Group Policy to restrict file and directory permissions can prevent unauthorized modifications to W32Time DLLs, blocking the insertion of malicious code. Simultaneously, restricting registry permissions through Group Policy is crucial for safeguarding W32Time registry settings against unauthorized changes.