Detection: Windows RunMRU Command Execution

Updated Date: 2024-11-08 ID: a15aa1ab-2b79-467f-8201-65e0f32d5b1a Author: Nasreddine Bencherchali, Michael Haag, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects modifications to the Windows RunMRU registry key, which stores a history of commands executed through the Run dialog box (Windows+R). It leverages Endpoint Detection and Response (EDR) telemetry to monitor registry events targeting this key. This activity is significant as malware often uses the Run dialog to execute malicious commands while attempting to appear legitimate. If confirmed malicious, this could indicate an attacker using indirect command execution techniques for defense evasion or persistence. The detection excludes MRUList value changes to focus on actual command entries.

Search

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Registry where Registry.registry_key_name="*\\Microsoft\\Windows\\CurrentVersion\\Explorer\\RunMRU*" NOT Registry.registry_key_name="*\\MRUList" by Registry.dest Registry.registry_value_data Registry.action  Registry.process_guid Registry.process_id Registry.registry_key_name Registry.user 
3| `drop_dm_object_name(Registry)` 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)` 
6| `windows_runmru_command_execution_filter`

Data Source

No data sources specified for this detection.

Macros Used

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

windows_runmru_command_execution_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
T1202	Indirect Command Execution	Defense Evasion

KillChainPhase.EXPLOITAITON

NistCategory.DE_AE

Cis18Value.CIS_10

Lazarus Group

RedCurl

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

The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the Registry node of the Endpoint data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.

Known False Positives

This detection may generate a few false positives, such as legitimate software updates or legitimate system maintenance activities that modify the RunMRU key. However, the exclusion of MRUList value changes helps reduce the number of false positives by focusing only on actual command entries. Add any specific false positives to the built in filter to reduce notables as needed.

Associated Analytic Story

Lumma Stealer

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
An instance of $registry_value_data$ was identified on endpoint $dest$ by user $user$ attempting to execute a command through the Run dialog box.	48	80	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

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: 1