Detecting Malicious Scheduled Tasks with Sysmon

Overview

Adversaries abuse Windows Task Scheduler (schtasks.exe, at.exe) for persistence (T1053.005) and lateral movement. Sysmon Event ID 1 captures schtasks.exe process creation with full command-line arguments, while Event ID 11 captures task XML files written to C:\Windows\System32\Tasks. Windows Security Event 4698 logs task registration details. This skill covers building detection rules that correlate these events to identify malicious scheduled tasks created from suspicious paths, with encoded payloads, or targeting remote systems.

Prerequisites

• Sysmon installed with a detection-focused configuration (e.g., SwiftOnSecurity or Olaf Hartong)
• Windows Event Log forwarding to SIEM (Splunk, Elastic, or Sentinel)
• PowerShell ScriptBlock Logging enabled (Event 4104)

Steps

1. Configure Sysmon to log Event IDs 1, 11, 12, 13 with task-related filters
2. Build detection rules for schtasks.exe /create with suspicious arguments
3. Correlate Event 4698 (task registered) with Sysmon Event 1 (process create)
4. Hunt for tasks executing from public directories or with encoded commands
5. Alert on remote task creation (schtasks /s) for lateral movement detection

Expected Output

[CRITICAL] Suspicious Scheduled Task Detected
  Task: \Microsoft\Windows\UpdateCheck
  Command: powershell.exe -enc SQBuAHYAbwBrAGUALQBXAGUAYgBSAGU...
  Created By: DOMAIN\compromised_user
  Parent Process: cmd.exe (PID 4532)
  Source: \\192.168.1.50 (remote creation)
  MITRE: T1053.005 - Scheduled Task/Job