Windows EFI Volume Mount Attempt Via Mountvol

name: Windows EFI Volume Mount Attempt Via Mountvol
id: 6ee1d152-56c7-40e8-8db0-edb0074a6bb2
version: 2
creation_date: '2021-12-08'
modification_date: '2026-05-13'
author: Raven Tait, Splunk
status: production
type: Anomaly
description: |-
    Detects attempts to mount the EFI volume.
    The EFI system partition (ESP) is a special partition on a data storage device (usually a hard disk drive or solid-state drive) that computers adhering to the UEFI (Unified Extensible Firmware Interface) specification use to store data necessary for the system to boot, such as bootloaders, device drivers, and system utilities.
    This is used with attacks such as PKFail to modify the system on boot.
data_source:
    - Sysmon EventID 1
    - Windows Event Log Security 4688
    - CrowdStrike ProcessRollup2
search: |-
    | tstats `security_content_summariesonly`
      count min(_time) as firstTime
            max(_time) as lastTime
    
    from datamodel=Endpoint.Processes where
    
    (
        Processes.process_name="mountvol.exe"
        OR
        Processes.original_file_name="MOUNTVOL.EXE"
    )
    Processes.process IN ("*-S*", "* /S*")
    
    by Processes.process Processes.vendor_product Processes.user_id Processes.process_hash
       Processes.parent_process_name Processes.parent_process_exec Processes.action
       Processes.dest Processes.process_current_directory Processes.process_path
       Processes.process_integrity_level Processes.original_file_name Processes.parent_process
       Processes.parent_process_path Processes.parent_process_guid Processes.parent_process_id
       Processes.process_guid Processes.process_id Processes.user Processes.process_name
    
    | `drop_dm_object_name(Processes)`
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    | `windows_efi_volume_mount_attempt_via_mountvol_filter`
how_to_implement: 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 `Processes` 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: Mounting the EFI volume can be part of normal system updates or legitimate maintenance tasks. Monitor for unusual timing or context to reduce false alerts.
references:
    - https://www.binarly.io/blog/pkfail-untrusted-platform-keys-undermine-secure-boot-on-uefi-ecosystem
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 20
          message: Potential EFI Volume Mount Attempt by $user$ via $process$ observed on $dest$.
threat_objects:
    - field: parent_process_name
      type: parent_process_name
    - field: process
      type: process
    - field: process_name
      type: process_name
analytic_story:
    - Compromised Windows Host
asset_type: Endpoint
mitre_attack_id:
    - T1204.002
    - T1542
    - T1688
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint