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 \
- Filter - WQL Query for the events we want. EventID = 19 \
- Consumer - An action to take upon triggering the filter. EventID = 20 \
- 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
Kill Chain Phase
- Actions on Objectives
- CIS 3
- CIS 5
1 2 3 4 `sysmon` EventCode=21 | rename host as dest | table _time, dest, user, Operation, EventType, Query, Consumer, Filter | `wmi_permanent_event_subscription___sysmon_filter`
The SPL above uses the following Macros:
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.
List of fields required to use this analytic.
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
|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.
source | version: 3