Detection: PowerShell Loading DotNET into Memory via Reflection

Description

The following analytic detects the use of PowerShell scripts to load .NET assemblies into memory via reflection, a technique often used in malicious activities such as those by Empire and Cobalt Strike. It leverages PowerShell Script Block Logging (EventCode=4104) to capture and analyze the full command executed. This behavior is significant as it can indicate advanced attack techniques aiming to execute code in memory, bypassing traditional defenses. If confirmed malicious, this activity could lead to unauthorized code execution, privilege escalation, and persistent access within the environment.

1`powershell` EventCode=4104 ScriptBlockText IN ("*Reflection.Assembly]::Load*", "*Reflection.Assembly.Load*", "*UnsafeLoadFrom*", "*.LoadFrom(*", "*.LoadModule(*", "*.LoadWithPartialName*", "*ReflectionOnlyLoad*") 
2| stats count min(_time) as firstTime max(_time) as lastTime by Opcode Computer UserID EventCode ScriptBlockText 
3| rename Computer as dest, UserID as user
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| `powershell_loading_dotnet_into_memory_via_reflection_filter`

Data Source

Name Platform Sourcetype Source
Powershell Script Block Logging 4104 Windows icon Windows 'xmlwineventlog' 'XmlWinEventLog:Microsoft-Windows-PowerShell/Operational'

Macros Used

Name Value
powershell (source=WinEventLog:Microsoft-Windows-PowerShell/Operational OR source="XmlWinEventLog:Microsoft-Windows-PowerShell/Operational")
powershell_loading_dotnet_into_memory_via_reflection_filter search *
powershell_loading_dotnet_into_memory_via_reflection_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1059 Command and Scripting Interpreter Execution
T1059.001 PowerShell Execution
Installation
DE.AE
CIS 10

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Risk Event True
This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

To successfully implement this analytic, you will need to enable PowerShell Script Block Logging on some or all endpoints. Additional setup here https://docs.splunk.com/Documentation/UBA/5.0.4.1/GetDataIn/AddPowerShell#Configure_module_logging_for_PowerShell.

Known False Positives

False positives should be limited as day to day scripts do not use this method.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

A suspicious powershell script contains reflective class assembly command in $ScriptBlockText$ to load .net code in memory with EventCode $EventCode$ in host $dest$

Risk Object Risk Object Type Risk Score Threat Objects
dest system 56 No Threat Objects
user user 56 No Threat Objects

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation Passing N/A N/A N/A
Unit Passing Dataset XmlWinEventLog:Microsoft-Windows-PowerShell/Operational XmlWinEventLog
Integration ✅ Passing Dataset XmlWinEventLog:Microsoft-Windows-PowerShell/Operational XmlWinEventLog

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range


Source: GitHub | Version: 6