WMI Permanent Event Subscription - Sysmon

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Description

This analytic looks for the creation of WMI permanent event subscriptions. The following analytic identifies the use of WMI Event Subscription to establish persistence or perform privilege escalation. WMI can be used to install event filters, providers, consumers, and bindings that execute code when a defined event occurs. WMI subscription execution is proxied by the WMI Provider Host process (WmiPrvSe.exe) and thus may result in elevated SYSTEM privileges. This analytic is restricted by commonly added process execution and a path. If the volume is low enough, remove the values and flag on any new subscriptions.
All event subscriptions have three components \

1. Filter - WQL Query for the events we want. EventID = 19 \
2. Consumer - An action to take upon triggering the filter. EventID = 20 \
3. Binding - Registers a filter to a consumer. EventID = 21
   Monitor for the creation of new WMI EventFilter, EventConsumer, and FilterToConsumerBinding. It may be pertinent to review all 3 to identify the flow of execution. In addition, EventCode 4104 may assist with any other PowerShell script usage that registered the subscription.

• Type: TTP

• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud

• Last Updated: 2020-12-08
• Author: Rico Valdez, Michael Haag, Splunk
• ID: ad05aae6-3b2a-4f73-af97-57bd26cee3b9

Annotations

ATT&CK

ATT&CK

ID	Technique	Tactic
T1546.003	Windows Management Instrumentation Event Subscription	Privilege Escalation, Persistence

T1546

Event Triggered Execution

Privilege Escalation, Persistence

Kill Chain Phase

• Exploitation
• Installation

NIST

• DE.CM

CIS20

• CIS 10

CVE

Search

`sysmon` EventCode=21 
| rename host as dest 
| table _time, dest, user, Operation, EventType, Query, Consumer, Filter 
| `wmi_permanent_event_subscription___sysmon_filter`

Macros

The SPL above uses the following Macros:

• sysmon

wmi_permanent_event_subscription_-_sysmon_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required fields

List of fields required to use this analytic.

• _time
• EventCode
• host
• user
• Operation
• EventType
• Query
• Consumer
• Filter

How To Implement

To successfully implement this search, you must be collecting Sysmon data using Sysmon version 6.1 or greater and have Sysmon configured to generate alerts for WMI activity (eventID= 19, 20, 21). In addition, you must have at least version 6.0.4 of the Sysmon TA installed to properly parse the fields.

Known False Positives

Although unlikely, administrators may use event subscriptions for legitimate purposes.

Associated Analytic Story

• Suspicious WMI Use

RBA

Risk Score	Impact	Confidence	Message
30.0	30	100	User $user$ on $host$ executed the following suspicious WMI query: $Query$. Filter: $filter$. Consumer: $Consumer$. EventCode: $EventCode$

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

• https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1546.003/T1546.003.md
• https://www.eideon.com/2018-03-02-THL03-WMIBackdoors/
• https://github.com/trustedsec/SysmonCommunityGuide/blob/master/chapters/WMI-events.md
• https://in.security/2019/04/03/an-intro-into-abusing-and-identifying-wmi-event-subscriptions-for-persistence/

Test Dataset

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

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