How to Detect and Analyze Suspicious PowerShell Command Execution
PowerShell is a powerful tool often exploited by attackers for malicious activities such as downloading malware, executing scripts, or interacting with remote systems. Detecting suspicious PowerShell usage requires monitoring key logs and correlating activity across systems.
1. Enable and Review PowerShell Logging
What to Do:
Enable Logging:
Script Block Logging (Event ID 4104): Captures the content of executed PowerShell scripts.
Module Logging: Tracks the execution of PowerShell modules for detailed analysis.
Analyze Logs:
Look for:
Suspicious commands.
Obfuscation techniques, such as splitting commands or using escape characters.
Encoded strings that may hide malicious payloads.
Red Flags: Scripts with heavy obfuscation, Base64 encoding, or references to downloading or executing external content.
2. Check for Use of Dangerous Cmdlets
What to Look For:
Dangerous Cmdlets:
Cmdlets commonly abused by attackers include:
Invoke-WebRequestInvoke-ExpressionAdd-Type.DownloadFile()
Behavior Patterns:
Commands indicating attempts to download or execute files from remote locations.
Red Flags: Cmdlets used in contexts or by accounts not typically requiring them, especially combined with suspicious URLs or payloads.
3. Monitor for Base64 Encoded Commands
What to Look For:
Encoded Commands:
Command lines containing
-EncodedCommand, often used to hide malicious scripts.
Decoding Activity:
Decode Base64-encoded strings to reveal the script’s actual intent.
Tools: Use decoding tools or PowerShell itself to translate Base64 strings for analysis.
Red Flags: Encoded commands that download, execute, or manipulate files in unexpected ways.
4. Investigate Scripts Run from Unusual Locations
What to Look For:
Execution Paths:
Event ID 4688: Tracks process creation. Look for PowerShell executed from:
Temporary directories (
%TEMP%,%APPDATA%).User-specific folders not typically associated with administrative scripts.
Command Context:
Correlate the script’s path with its command-line arguments for further validation.
Red Flags: Scripts running from non-standard locations, especially during non-business hours or by non-administrative accounts.
5. Cross-Reference with Network Logs
What to Do:
Correlate Logs:
Match PowerShell activity with outbound network traffic logs.
Look for connections to:
Unfamiliar IPs.
Malicious or newly registered domains.
Network Indicators:
Excessive outbound traffic immediately following suspicious PowerShell commands.
Red Flags: Connections to foreign or untrusted IPs/domains immediately after executing suspicious commands.
6. Immediate Response
What to Do:
Terminate the Process:
Stop the suspicious PowerShell process to prevent further execution.
Isolate the System:
Disconnect the affected machine from the network to contain the threat.
Investigate the Script:
Analyze the script to determine its purpose, intent, and potential impact.
Strengthen Security Controls:
Tighten PowerShell execution policies:
Restrict to signed scripts only.
Enforce Constrained Language Mode for non-administrative users.
Implement application whitelisting to block unauthorized script execution.
Post-Incident Actions:
Enhance Monitoring:
Deploy detection rules in SIEM tools for:
Obfuscated PowerShell usage.
Specific dangerous cmdlets.
Enable alerting for patterns consistent with known attack techniques.
Educate Users and Admins:
Train teams on secure PowerShell usage and recognizing suspicious activity.
Conclusion
Detecting suspicious PowerShell activity involves monitoring for unusual execution patterns, encoded commands, and unauthorized script usage. Proactive measures, such as enabling comprehensive logging and implementing strict execution policies, ensure robust detection and response capabilities.
Last updated