Detection: Powershell Using memory As Backing Store

Updated Date: 2024-09-30 ID: c396a0c4-c9f2-11eb-b4f5-acde48001122 Author: Teoderick Contreras, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects suspicious PowerShell script execution using memory streams as a backing store, identified via EventCode 4104. It leverages PowerShell Script Block Logging to capture scripts that create new objects with memory streams, often used to decompress and execute payloads in memory. This activity is significant as it indicates potential in-memory execution of malicious code, bypassing traditional file-based detection. If confirmed malicious, this technique could allow attackers to execute arbitrary code, maintain persistence, or escalate privileges without leaving a trace on the disk.

Search

1`powershell` EventCode=4104 ScriptBlockText = *New-Object* ScriptBlockText = *IO.MemoryStream* 
2| stats count min(_time) as firstTime max(_time) as lastTime by EventCode ScriptBlockText Computer UserID 
3| rename Computer as dest 
4| rename UserID as user 
5| `security_content_ctime(firstTime)` 
6| `security_content_ctime(lastTime)` 
7| `powershell_using_memory_as_backing_store_filter`

Data Source

Name	Platform	Sourcetype	Source
Powershell Script Block Logging 4104	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_using_memory_as_backing_store_filter	`search *`

powershell_using_memory_as_backing_store_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
T1059.001	PowerShell	Execution
T1059	Command and Scripting Interpreter	Execution

KillChainPhase.INSTALLATION

NistCategory.DE_CM

Cis18Value.CIS_10

APT19

APT28

APT29

APT3

APT32

APT33

APT38

APT39

APT41

APT5

Aquatic Panda

BRONZE BUTLER

Blue Mockingbird

CURIUM

Chimera

Cinnamon Tempest

Cobalt Group

Confucius

CopyKittens

Daggerfly

DarkHydrus

DarkVishnya

Deep Panda

Dragonfly

Earth Lusca

Ember Bear

FIN10

FIN13

FIN6

FIN7

FIN8

Fox Kitten

GALLIUM

GOLD SOUTHFIELD

Gallmaker

Gamaredon Group

Gorgon Group

HAFNIUM

HEXANE

Inception

Indrik Spider

Kimsuky

Lazarus Group

LazyScripter

Leviathan

Magic Hound

Molerats

MoustachedBouncer

MuddyWater

Mustang Panda

Nomadic Octopus

OilRig

Patchwork

Play

Poseidon Group

RedCurl

Saint Bear

Sandworm Team

Sidewinder

Silence

Stealth Falcon

TA2541

TA459

TA505

TeamTNT

Threat Group-3390

Thrip

ToddyCat

Tonto Team

Turla

Volt Typhoon

WIRTE

Winter Vivern

Wizard Spider

menuPass

APT19

APT32

APT37

APT39

Dragonfly

FIN5

FIN6

FIN7

Fox Kitten

Ke3chang

OilRig

Saint Bear

Stealth Falcon

Whitefly

Windigo

Winter Vivern

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 Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

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

powershell may used this function to store out object into memory.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
A PowerShell script contains memorystream command on host $dest$.	40	50	80

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

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: 4