Detection: Windows ISO LNK File Creation

Updated Date: 2024-05-09 ID: d7c2c09b-9569-4a9e-a8b6-6a39a99c1d32 Author: Michael Haag, Teoderick Contreras, Splunk Type: Hunting Product: Splunk Enterprise Security

Description

The following analytic detects the creation of .iso.lnk files in the %USER%\AppData\Local\Temp<random folder name>\ path, indicating that an ISO file has been mounted and accessed. This detection leverages the Endpoint.Filesystem data model, specifically monitoring file creation events in the Windows Recent folder. This activity is significant as it may indicate the delivery and execution of potentially malicious payloads via ISO files. If confirmed malicious, this could lead to unauthorized code execution, data exfiltration, or further system compromise.

Search

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Filesystem where Filesystem.file_path IN ("*\\Microsoft\\Windows\\Recent\\*") Filesystem.file_name IN ("*.iso.lnk", "*.img.lnk", "*.vhd.lnk", "*vhdx.lnk") by Filesystem.file_create_time Filesystem.process_id Filesystem.file_name Filesystem.file_path Filesystem.dest 
3| `drop_dm_object_name(Filesystem)` 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| `windows_iso_lnk_file_creation_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
Sysmon EventID 11	Windows	`'xmlwineventlog'`	`'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'`	N/A

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
windows_iso_lnk_file_creation_filter	`search *`

windows_iso_lnk_file_creation_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
T1566.001	Spearphishing Attachment	Initial Access
T1566	Phishing	Initial Access
T1204.001	Malicious Link	Execution
T1204	User Execution	Execution

KillChainPhase.DELIVERY

KillChainPhase.INSTALLATION

NistCategory.DE_AE

Cis18Value.CIS_10

APT-C-36

APT1

APT12

APT19

APT28

APT29

APT30

APT32

APT33

APT37

APT38

APT39

APT41

Ajax Security Team

Andariel

BITTER

BRONZE BUTLER

BlackTech

Cobalt Group

Confucius

DarkHydrus

Darkhotel

Dragonfly

EXOTIC LILY

Elderwood

Ember Bear

FIN4

FIN6

FIN7

FIN8

Ferocious Kitten

Gallmaker

Gamaredon Group

Gorgon Group

Higaisa

Inception

IndigoZebra

Kimsuky

Lazarus Group

LazyScripter

Leviathan

Machete

Malteiro

Mofang

Molerats

MuddyWater

Mustang Panda

Naikon

Nomadic Octopus

OilRig

PLATINUM

Patchwork

RTM

Rancor

Sandworm Team

SideCopy

Sidewinder

Silence

TA2541

TA459

TA505

TA551

The White Company

Threat Group-3390

Tonto Team

Transparent Tribe

Tropic Trooper

WIRTE

Windshift

Wizard Spider

admin@338

menuPass

Axiom

GOLD SOUTHFIELD

APT28

APT29

APT3

APT32

APT33

APT39

BlackTech

Cobalt Group

Confucius

EXOTIC LILY

Earth Lusca

Elderwood

Ember Bear

Evilnum

FIN4

FIN7

FIN8

Kimsuky

LazyScripter

Leviathan

LuminousMoth

Machete

Magic Hound

Mofang

Molerats

MuddyWater

Mustang Panda

Mustard Tempest

OilRig

Patchwork

Sandworm Team

Sidewinder

TA2541

TA505

Transparent Tribe

Turla

Windshift

Wizard Spider

ZIRCONIUM

LAPSUS$

Scattered Spider

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	False

This configuration file applies to all detections of type hunting.

Implementation

To successfully implement this search you need to be ingesting information on process that include the name of the process responsible for the changes from your endpoints into the Endpoint datamodel in the Filesystem node. In addition, confirm the latest CIM App 4.20 or higher is installed and the latest TA for the endpoint product.

Known False Positives

False positives may be high depending on the environment and consistent use of ISOs mounting. Restrict to servers, or filter out based on commonly used ISO names. Filter as needed.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
An ISO file was mounted on $dest$ and should be reviewed and filtered as needed.	40	80	50

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-Sysmon/Operational`	`xmlwineventlog`
Integration	✅ Passing	Dataset	`XmlWinEventLog:Microsoft-Windows-Sysmon/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