xalgord Detecting Suspicious Powershell Execution
When to Use
- When proactively hunting for indicators of detecting suspicious powershell execution in the environment
- After threat intelligence indicates active campaigns using these techniques
- During incident response to scope compromise related to these techniques
- When EDR or SIEM alerts trigger on related indicators
- During periodic security assessments and purple team exercises
Detection Gaps & Validation
- Script Block Logging (4104) is the ground truth: EID 4104 captures the deobfuscated script. With the GPO off you only have 4688/Sysmon EID 1 command lines, which obfuscation defeats — confirm 4104 and 4103 (Module Logging) are enabled and forwarded.
-EncodedCommandand aliases: rules keyed on the literalpowershell.exe -encmiss-e,-ec,pwsh, and renamed/copied binaries — match on EID 1OriginalFileName = PowerShell.EXEplus base64 entropy, not the image name.- AMSI bypass + downgrade:
[Ref].Assembly...amsiInitFailedand-Version 2downgrade attacks evade AMSI/4104; theMicrosoft-Windows-PowerShellETW provider can be patched out in-process — treat a host that suddenly stops emitting 4104 as suspicious, not clean. - LOLBin proxies:
IEX (New-Object Net.WebClient).DownloadStringand execution viamsbuild/installutilsidestep powershell.exe. - Validate: run Atomic Red Team T1059.001 (encoded command + download cradle) and confirm the 4104 keyword and encoded-command searches fire.
- Tune FPs: SCCM, Intune, and admin automation generate encoded/long PowerShell — baseline by signing cert and parent (allow
WmiPrvSE/ccmexecparents) before alerting.
Prerequisites
- EDR platform with process and network telemetry (CrowdStrike, MDE, SentinelOne)
- SIEM with relevant log data ingested (Splunk, Elastic, Sentinel)
- Sysmon deployed with comprehensive configuration
- Windows Security Event Log forwarding enabled
- Threat intelligence feeds for IOC correlation
Workflow
- Formulate Hypothesis: Define a testable hypothesis based on threat intelligence or ATT&CK gap analysis.
- Identify Data Sources: Determine which logs and telemetry are needed to validate or refute the hypothesis.
- Execute Queries: Run detection queries against SIEM and EDR platforms to collect relevant events.
- Analyze Results: Examine query results for anomalies, correlating across multiple data sources.
- Validate Findings: Distinguish true positives from false positives through contextual analysis.
- Correlate Activity: Link findings to broader attack chains and threat actor TTPs.
- Document and Report: Record findings, update detection rules, and recommend response actions.
Key Concepts
| Concept | Description |
|---|---|
| T1059.001 | PowerShell |
| T1059.003 | Windows Command Shell |
| T1562.001 | Disable or Modify Tools |
Tools & Systems
| Tool | Purpose |
|---|---|
| CrowdStrike Falcon | EDR telemetry and threat detection |
| Microsoft Defender for Endpoint | Advanced hunting with KQL |
| Splunk Enterprise | SIEM log analysis with SPL queries |
| Elastic Security | Detection rules and investigation timeline |
| Sysmon | Detailed Windows event monitoring |
| Velociraptor | Endpoint artifact collection and hunting |
| Sigma Rules | Cross-platform detection rule format |
Common Scenarios
- Scenario 1: Base64 encoded PowerShell command launched by macro document
- Scenario 2: IEX download cradle fetching payload from C2 server
- Scenario 3: AMSI bypass via reflection patching before payload execution
- Scenario 4: PowerShell Empire agent communicating with C2
Output Format
Hunt ID: TH-DETECT-[DATE]-[SEQ]
Technique: T1059.001
Host: [Hostname]
User: [Account context]
Evidence: [Log entries, process trees, network data]
Risk Level: [Critical/High/Medium/Low]
Confidence: [High/Medium/Low]
Recommended Action: [Containment, investigation, monitoring]