Windows: PowerShell Core DLL Loaded By Non PowerShell Process

Rule ID

PH_Rule_SIGMA_2013

Default Status

Enabled

Description

Detects loading of essential DLLs used by PowerShell, but not by the process powershell.exe. Detects behaviour similar to meterpreter's "load powershell" extension. This rule is adapted from https://github.com/SigmaHQ/sigma/blob/master/rules/windows/image_load/image_load_dll_system_management_automation_susp_load.yml

Severity

MITRE ATT&CK® Tactics

Execution

Execution consists of techniques that result in adversary-controlled code running on a local or remote system. Techniques that run malicious code are often paired with techniques from all other tactics to achieve broader goals, like exploring a network or stealing data. For example, an adversary might use a remote access tool to run a PowerShell script that does Remote System Discovery.

https://attack.mitre.org/tactics/TA0002

MITRE ATT&CK® Techniques

T1059.001

Command and Scripting Interpreter: PowerShell

Adversaries may abuse PowerShell commands and scripts for execution. Adversaries can use PowerShell to perform a number of actions, including discovery of information and execution of code.

https://attack.mitre.org/techniques/T1059/001

Impacts

Server

Data Source

Windows Sysmon via FortiSIEM Agent

Detection

Correlation

Remediation Guidance

No remediation guidance specified

Time Window

If the following pattern or patterns match an ingested event within the given time window in seconds, trigger an incident.

300 seconds

Trigger Conditions

If the following defined pattern/s occur within a 300 second time window.

Filter

SubPattern Definitions

SubPattern Name: Filter

This is the named definition of the event query, this is important if multiple subpatterns are defined to distinguish them.

SubPattern Query

This is the query logic that matches incoming events

eventType="Win-Sysmon-7-Image-Loaded" AND loadedProcName REGEXP "\\System\.Management\.Automation\.Dll$|\\System\.Management\.Automation\.ni\.Dll$" AND ((procName NOT IN ("C:\\Program Files\\PowerShell\\7\\pwsh.exe","C:\\Windows\\System32\\dsac.exe") AND procName NOT REGEXP "\\Citrix\\ConfigSync\\ConfigSyncRun\.exe$|\\IDE\\devenv\.exe$|\\Microsoft SQL Server Management Studio .*\\Common.*\\IDE\\Ssms\.exe$|\\ServerManager\.exe$|\\ServiceHub\.Host\.CLR\.x86\.exe$|\\ServiceHub\.SettingsHost\.exe$|\\ServiceHub\.VSDetouredHost\.exe$|\\WINDOWS\\System32\\RemoteFXvGPUDisablement\.exe$|\\WINDOWS\\System32\\sdiagnhost\.exe$|\\mscorsvw\.exe$|\\powershell\.exe$|\\powershell_ise\.exe$|\\runscripthelper\.exe$|\\sqlps\.exe$|\\syncappvpublishingserver\.exe$|\\winrshost\.exe$|\\wsmprovhost\.exe$" AND procName NOT REGEXP "^C:\\Program Files \(x86\)\\Microsoft Visual Studio\\|^C:\\Program Files\\Microsoft Visual Studio\\") AND (procName NOT REGEXP "^C:\\Windows\\Temp\\asgard2-agent\\" OR procName NOT REGEXP "\\thor64\.exe$|\\thor\.exe$") AND (procName IS NOT NULL))

Group by Attributes

This defines how matching events are aggregated, only events with the same matching attribute values are grouped into one unique incident ID

hostName,loadedProcName,procName

Aggregate Constraint

This is most typically a numerical constraint that defines when the rule should trigger an incident

COUNT(*) >= 1

Incident Attribute Mapping

This section defines which fields in matching raw events should be mapped to the incident attributes in the resulting incident.

The available raw event attributes to map are limited to the group by attributes and the aggregate event constraint fields for each subpattern

hostName = Filter.hostName,
loadedProcName = Filter.loadedProcName,
procName = Filter.procName

FortiSIEM Rules