at.exe

Superseded by schtasks.exe in later versions of Windows, understanding at.exe remains relevant for analyzing older systems.

at.exe is a command-line utility that enables users and administrators to schedule commands and programs to run on a local or remote computer at specified times. Its functionality is integral to automating system tasks, but it can also be exploited for persistence or execution of malicious payloads in older Windows environments.

• Image Path: Typically found in %SystemRoot%\system32\at.exe

• Expected Command Line: at [\\computername] [[id] [/delete] | /delete [/yes]]

  • at 15:00 cmd.exe /c "example_command" schedules example_command to run at 3:00 PM.

• Parent Process: Commonly initiated by cmd.exe or Task Scheduler service processes, but in malicious use cases, it could be spawned by any process.

• Number of Instances: Varies based on the number of scheduled tasks. Typically, at.exe runs briefly to schedule a task and then exits.

• User Account: Runs under the context of the user who schedules the task. Tasks scheduled to run at system startup or in a system context may require administrative privileges.

• Start Time: Execution time is determined by the scheduling parameters passed to the command.

Functionality

• File Management: While at.exe itself does not manage files, it can schedule tasks that perform file operations.

• User Interface: Primarily a command-line tool, offering no graphical user interface. Users interact with at.exe through the Windows Command Prompt.

• Registry Configuration: Does not directly modify the registry for its primary operation, but tasks scheduled with at.exe can be designed to interact with the registry.

• Multiple Instances: The nature of at.exe allows for multiple tasks to be scheduled, each potentially running different commands or applications at specified times.

Security Considerations

The use of at.exe for scheduling tasks presents several security considerations:

• Legacy Tool: As a legacy tool, at.exe may not be closely monitored by modern security solutions, making it a potential vector for stealthy execution of malicious tasks.

• Privilege Execution: Tasks scheduled with at.exe run with the permissions of the user who scheduled them, potentially allowing for privilege escalation if used by an administrator account.

• Malicious Use: Threat actors can exploit at.exe to schedule malicious tasks, maintaining persistence or executing malware at specific times.

• Auditing and Monitoring: Due to its potential for misuse, monitoring the execution of at.exe and scheduled tasks is crucial for security. Event logs and security solutions should be configured to alert on its use, especially in environments where at.exe is not commonly used for legitimate purposes.