Engine state is changed from None to Available

// EVENT DEFINITION:

The PowerShell host engine (`powershell.exe` or runspace host) initialized and started execution.

// DETAILED TELEMETRY & CONTEXT:

Event ID 400 (`Windows PowerShell` / `Operational`) records the initialization and startup of the PowerShell engine (`HostName`, `HostVersion`, `HostApplication`). When threat actors execute PowerShell via custom runspaces inside non-standard applications (`System.Management.Automation` hosted in `msbuild.exe` or `rundll32.exe`), event `400` reveals the anomalous `HostApplication` path.

[ ! ]Failure Reason / Root Cause Analysis

PowerShell runspace engine initialization (`HostApplication` command line shown).

Operational Metadata & Applicability

Log Category:PowerShell

Audit Type Classification:Success Audit

Supported Operating Systems:Windows Server 2016, 2019, 2022 / Windows Client 10, 11 (Enterprise / Pro)

Threat Hunting Keywords:

400powershell engine starthostapplicationunmanaged powershellrunspace startup

MITRE ATT&CK Framework Alignment

T1059.001

Command and Scripting Interpreter: PowerShellTactic: Execution

T1218

System Binary Proxy ExecutionTactic: Defense Evasion

Mitigation Playbook & Recommended SOC Actions

•Inspect `HostApplication`. Alert immediately if the PowerShell engine starts inside processes other than `powershell.exe`, `pwsh.exe`, `wsmprovhost.exe`, or standard management tools (`Unmanaged PowerShell runspace injection`).

Representative Windows Event XML Schema

<Event xmlns="http://schemas.microsoft.com/win/2004/08/events/event">
  <System>
    <Provider Name="Microsoft-Windows-Security-Auditing" Guid="{54849625-5478-4994-A5BA-3E3B0328C30D}" />
    <EventID>400</EventID>
    <Version>0</Version>
    <Level>0</Level>
    <Task>12544</Task>
    <Opcode>0</Opcode>
    <Keywords>0x8020000000000000</Keywords>
    <TimeCreated SystemTime="2026-07-17T09:54:44.230Z" />
    <EventRecordID>1048576</EventRecordID>
    <Correlation />
    <Execution ProcessID="612" ThreadID="1024" />
    <Channel>Security</Channel>
    <Computer>DC01.enterprise.internal</Computer>
    <Security />
  </System>
  <EventData>
    <Data Name="SubjectUserSid">S-1-5-18</Data>
    <Data Name="SubjectUserName">SYSTEM</Data>
    <Data Name="SubjectDomainName">NT AUTHORITY</Data>
    <Data Name="SubjectLogonId">0x3e7</Data>
    <!-- Event telemetry fields specific to Engine state is changed from None to Available -->
  </EventData>
</Event>

Correlated / Related Security Event IDs

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