Detection: Windows EDRSilencer Execution

Description

Detects the usage of EDRSilencer. Inspired by the closed-source FireBlock tool from MdSec NightHawk, this custom tool was developed to block outbound traffic of running Endpoint Detection and Response (EDR) processes using Windows Filtering Platform (WFP) APIs. Its features include searching for running EDR processes and applying WFP filters to block outbound traffic, adding filters for specific processes, and removing filters either individually or globally. The tool includes a custom implementation to avoid file handle access issues with EDR processes by bypassing the CreateFileW API. It supports a wide range of EDRs, including Microsoft Defender, Carbon Black, SentinelOne, and more, though further testing on various EDRs is recommended. The tool has been tested on Windows 10 and Windows Server 2016, and its usage involves simple commands for blocking or unblocking traffic.

Search

 1
 2| tstats `security_content_summariesonly`
 3  count min(_time) as firstTime
 4        max(_time) as lastTime
 5
 6from datamodel=Endpoint.Processes where
 7
 8Processes.process_name="EDRSilencer.exe"
 9OR
10(
11    Processes.process="*blockedr *"
12    NOT Processes.process="*blockedreport*"
13)
14
15by Processes.process Processes.vendor_product Processes.user_id Processes.process_hash
16   Processes.parent_process_name Processes.parent_process_exec Processes.action
17   Processes.dest Processes.process_current_directory Processes.process_path
18   Processes.process_integrity_level Processes.original_file_name Processes.parent_process
19   Processes.parent_process_path Processes.parent_process_guid Processes.parent_process_id
20   Processes.process_guid Processes.process_id Processes.user Processes.process_name
21
22
23| `drop_dm_object_name(Processes)`
24
25| `security_content_ctime(firstTime)`
26
27| `security_content_ctime(lastTime)`
28
29| `windows_edrsilencer_execution_filter`

Data Source

Name	Platform	Sourcetype	Source
CrowdStrike ProcessRollup2	Other	'crowdstrike:events:sensor'	'crowdstrike'
Sysmon EventID 1	Windows	'XmlWinEventLog'	'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational'
Windows Event Log Security 4688	Windows	'XmlWinEventLog'	'XmlWinEventLog:Security'

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

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 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

Some legitimate administrative tools or security workflows may use similar techniques to block or filter EDR traffic for maintenance or troubleshooting. Verify the context and authorized use before flagging.

Associated Analytic Story

• Security Solution Tampering

Risk Based Analytics (RBA)

Risk Message:

Potential EDRSilencer execution observed on $dest$ via $process$.

References

• https://github.com/netero1010/EDRSilencer

Detection Testing

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