Detection: PowerShell WebRequest Using Memory Stream

Updated Date: 2024-09-30 ID: 103affa6-924a-4b53-aff4-1d5075342aab Author: Steven Dick Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects the use of .NET classes in PowerShell to download a URL payload directly into memory, a common fileless malware staging technique. It leverages PowerShell Script Block Logging (EventCode=4104) to identify suspicious PowerShell commands involving system.net.webclient, system.net.webrequest, and IO.MemoryStream. This activity is significant as it indicates potential fileless malware execution, which is harder to detect and can bypass traditional file-based defenses. If confirmed malicious, this technique could allow attackers to execute code in memory, evade detection, and maintain persistence in the environment.

Search

1`powershell` EventCode=4104  ScriptBlockText IN ("*system.net.webclient*","*system.net.webrequest*") AND ScriptBlockText="*IO.MemoryStream*" 
2| eval Path = case(isnotnull(Path),Path,true(),"unknown") 
3| stats count min(_time) as firstTime max(_time) as lastTime list(ScriptBlockText) as command values(Path) as file_name values(UserID) as user by ActivityID, Computer, EventCode 
4| rename Computer as dest, EventCode as signature_id 
5| `security_content_ctime(firstTime)` 
6| `security_content_ctime(lastTime)` 
7| `powershell_webrequest_using_memory_stream_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_webrequest_using_memory_stream_filter	`search *`

powershell_webrequest_using_memory_stream_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
T1105	Ingress Tool Transfer	Command And Control
T1027.011	Fileless Storage	Defense Evasion

KillChainPhase.COMMAND_AND_CONTROL

KillChainPhase.EXPLOITAITON

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

APT-C-36

APT18

APT28

APT29

APT3

APT32

APT33

APT37

APT38

APT39

APT41

Ajax Security Team

Andariel

Aquatic Panda

BITTER

BRONZE BUTLER

BackdoorDiplomacy

Chimera

Cinnamon Tempest

Cobalt Group

Confucius

Daggerfly

Darkhotel

Dragonfly

Elderwood

Evilnum

FIN13

FIN7

FIN8

Fox Kitten

GALLIUM

Gamaredon Group

Gorgon Group

HAFNIUM

HEXANE

INC Ransom

IndigoZebra

Indrik Spider

Ke3chang

Kimsuky

Lazarus Group

LazyScripter

Leviathan

LuminousMoth

Magic Hound

Metador

Molerats

Moonstone Sleet

Moses Staff

MuddyWater

Mustang Panda

Mustard Tempest

Nomadic Octopus

OilRig

PLATINUM

Patchwork

Play

Rancor

Rocke

Sandworm Team

SideCopy

Sidewinder

Silence

TA2541

TA505

TA551

TeamTNT

Threat Group-3390

Tonto Team

Tropic Trooper

Turla

Volatile Cedar

Volt Typhoon

WIRTE

Whitefly

Windshift

Winnti Group

Winter Vivern

Wizard Spider

ZIRCONIUM

menuPass

APT32

Turla

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

The following analytic requires PowerShell operational logs to be imported. Modify the powershell macro as needed to match the sourcetype or add index. This analytic is specific to 4104, or PowerShell Script Block Logging.

Known False Positives

Unknown, possible custom scripting.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
Powershell webrequest to memory stream behavior. Possible fileless malware staging on $dest$ by $user$.	80	100	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: 3