Detection: Windows Raw Access To Master Boot Record Drive

Updated Date: 2025-05-02 ID: 7b83f666-900c-11ec-a2d9-acde48001122 Author: Teoderick Contreras, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects suspicious raw access reads to the drive containing the Master Boot Record (MBR). It leverages Sysmon EventCode 9 to identify processes attempting to read or write to the MBR sector, excluding legitimate system processes. This activity is significant because adversaries often target the MBR to wipe, encrypt, or overwrite it as part of their impact payload. If confirmed malicious, this could lead to system instability, data loss, or a complete system compromise, severely impacting the organization's operations.

Search

1`sysmon` EventCode=9 Device = \\Device\\Harddisk0\\DR0 NOT (Image IN("*\\Windows\\System32\\*", "*\\Windows\\SysWOW64\\*")) 
2| stats count min(_time) as firstTime max(_time) as lastTime by dest dvc process_exec process_guid process_id process_name process_path signature signature_id user_id vendor_product Device Image 
3| `security_content_ctime(firstTime)` 
4| `security_content_ctime(lastTime)` 
5| `windows_raw_access_to_master_boot_record_drive_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon EventID 9	Windows	`'xmlwineventlog'`	`'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'`

Macros Used

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

windows_raw_access_to_master_boot_record_drive_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
T1561.002	Disk Structure Wipe	Impact

Actions on Objectives

DE.CM

CIS 10

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 logs with the raw access read event (like sysmon eventcode 9), process name and process guid from your endpoints. If you are using Sysmon, you must have at least version 6.0.4 of the Sysmon TA.

Known False Positives

There are som minimal number of normal applications from system32 folder like svchost.exe accessing the MBR. In this case we used 'system32' and 'syswow64' path as a filter for this detection.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

process accessing MBR $Device$ on $dest$

Risk Object	Risk Object Type	Risk Score	Threat Objects
dest	system	90	No Threat Objects

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: 7