Scheduled Task/Job: At (Windows)

Adversaries may abuse the at.exe utility to perform task scheduling for initial or recurring execution of malicious code. The at utility exists as an executable within Windows for scheduling tasks at a specified time and date. Using at requires that the Task Scheduler service be running, and the user to be logged on as a member of the local Administrators group.

An adversary may use at.exe in Windows environments to execute programs at system startup or on a scheduled basis for persistence. at can also be abused to conduct remote Execution as part of Lateral Movement and or to run a process under the context of a specified account (such as SYSTEM).

Note: The at.exe command line utility has been deprecated in current versions of Windows in favor of schtasks.

ID: T1053.002
Sub-technique of:  T1053
Tactics: Execution, Persistence, Privilege Escalation
Platforms: Windows
Permissions Required: Administrator
Data Sources: File monitoring, Process command-line parameters, Process monitoring, Windows event logs
Supports Remote:  Yes
Version: 1.0
Created: 27 November 2019
Last Modified: 24 March 2020

Procedure Examples

Name Description
APT18

APT18 actors used the native at Windows task scheduler tool to use scheduled tasks for execution on a victim network.[9]

at

at can be used to schedule a task on a system.[5]

BRONZE BUTLER

BRONZE BUTLER has used at to register a scheduled task to execute malware during lateral movement.[7]

MURKYTOP

MURKYTOP has the capability to schedule remote AT jobs.[6]

Threat Group-3390

Threat Group-3390 actors use at to schedule tasks to run self-extracting RAR archives, which install HTTPBrowser or PlugX on other victims on a network.[8]

Mitigations

Mitigation Description
Audit

Toolkits like the PowerSploit framework contain PowerUp modules that can be used to explore systems for permission weaknesses in scheduled tasks that could be used to escalate privileges. [3] Windows operating system also creates a registry key specifically associated with the creation of a scheduled task on the destination host at: Microsoft\Windows NT\CurrentVersion\Schedule\TaskCache\Tree\At1. [4]

Operating System Configuration

Configure settings for scheduled tasks to force tasks to run under the context of the authenticated account instead of allowing them to run as SYSTEM. The associated Registry key is located at HKLM\SYSTEM\CurrentControlSet\Control\Lsa\SubmitControl. The setting can be configured through GPO: Computer Configuration > [Policies] > Windows Settings > Security Settings > Local Policies > Security Options: Domain Controller: Allow server operators to schedule tasks, set to disabled. [2]

Privileged Account Management

Configure the Increase Scheduling Priority option to only allow the Administrators group the rights to schedule a priority process. This can be configured through GPO: Computer Configuration > [Policies] > Windows Settings > Security Settings > Local Policies > User Rights Assignment: Increase scheduling priority. [1]

User Account Management

Limit privileges of user accounts and remediate Privilege Escalation vectors so only authorized administrators can create scheduled tasks on remote systems.

Detection

Monitor process execution from the svchost.exe in Windows 10 and the Windows Task Scheduler taskeng.exe for older versions of Windows. [10] If scheduled tasks are not used for persistence, then the adversary is likely to remove the task when the action is complete. Monitor Windows Task Scheduler stores in %systemroot%\System32\Tasks for change entries related to scheduled tasks that do not correlate with known software, patch cycles, etc.

Configure event logging for scheduled task creation and changes by enabling the "Microsoft-Windows-TaskScheduler/Operational" setting within the event logging service. [11] Several events will then be logged on scheduled task activity, including: [12][13]

  • Event ID 106 on Windows 7, Server 2008 R2 - Scheduled task registered
  • Event ID 140 on Windows 7, Server 2008 R2 / 4702 on Windows 10, Server 2016 - Scheduled task updated
  • Event ID 141 on Windows 7, Server 2008 R2 / 4699 on Windows 10, Server 2016 - Scheduled task deleted
  • Event ID 4698 on Windows 10, Server 2016 - Scheduled task created
  • Event ID 4700 on Windows 10, Server 2016 - Scheduled task enabled
  • Event ID 4701 on Windows 10, Server 2016 - Scheduled task disabled

Tools such as Sysinternals Autoruns may also be used to detect system changes that could be attempts at persistence, including listing current scheduled tasks. [14]

Remote access tools with built-in features may interact directly with the Windows API to perform these functions outside of typical system utilities. Tasks may also be created through Windows system management tools such as Windows Management Instrumentation and PowerShell, so additional logging may need to be configured to gather the appropriate data.

References