Detection: Windows Modify Registry With MD5 Reg Key Name

Updated Date: 2024-05-25 ID: 4662c6b1-0754-455e-b9ff-3ee730af3ba8 Author: Teoderick Contreras, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects potentially malicious registry modifications characterized by MD5-like registry key names. It leverages the Endpoint data model to identify registry entries under the SOFTWARE path with 32-character hexadecimal names, a technique often used by NjRAT malware for fileless storage of keylogs and .DLL plugins. This activity is significant as it can indicate the presence of NjRAT or similar malware, which can lead to unauthorized data access and persistent threats within the environment. If confirmed malicious, attackers could maintain persistence and exfiltrate sensitive information.

Search

 1
 2| tstats `security_content_summariesonly`  count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Registry where  Registry.registry_path = "*\\SOFTWARE\\*" Registry.registry_value_data = "Binary Data" by Registry.dest Registry.user Registry.registry_path Registry.registry_value_name Registry.registry_value_data Registry.registry_key_name 
 3| `drop_dm_object_name(Registry)` 
 4| eval dropped_reg_path = split(registry_path, "\\") 
 5| eval dropped_reg_path_split_count = mvcount(dropped_reg_path) 
 6| eval validation_result= if(match(registry_value_name,"^[0-9a-fA-F]{32}$"),"md5","nonmd5") 
 7| where validation_result = "md5" AND dropped_reg_path_split_count <= 5 
 8| table dest user registry_path registry_value_name registry_value_data registry_key_name reg_key_name dropped_reg_path_split_count validation_result 
 9| `security_content_ctime(lastTime)` 
10| `security_content_ctime(firstTime)` 
11| `windows_modify_registry_with_md5_reg_key_name_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
Sysmon EventID 12	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_modify_registry_with_md5_reg_key_name_filter	`search *`

windows_modify_registry_with_md5_reg_key_name_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
T1112	Modify Registry	Defense Evasion

KillChainPhase.EXPLOITAITON

NistCategory.DE_CM

Cis18Value.CIS_10

APT19

APT32

APT38

APT41

Blue Mockingbird

Dragonfly

Earth Lusca

Ember Bear

FIN8

Gamaredon Group

Gorgon Group

Kimsuky

LuminousMoth

Magic Hound

Patchwork

Silence

TA505

Threat Group-3390

Turla

Wizard 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 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 search you need to be ingesting information on process that include the name of the Filesystem responsible for the changes from your endpoints into the Endpoint datamodel in the Filesystem node.

Known False Positives

unknown

Associated Analytic Story

NjRAT

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
A md5 registry value name $registry_value_name$ is created on $dest$	36	60	60

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

https://malpedia.caad.fkie.fraunhofer.de/details/win.njrat

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: 2