splunk-security_content/docs/_posts/2021-06-15-wevtutil_usage_to_disable_logs.md

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title	excerpt	categories	last_modified_at	toc	toc_label	tags
Wevtutil Usage To Disable Logs	Indicator Removal on Host, Clear Windows Event Logs	Endpoint	2021-06-15	true		Indicator Removal on Host Defense Evasion Clear Windows Event Logs Defense Evasion Splunk Behavioral Analytics Endpoint_Processes

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Description

This search is to detect execution of wevtutil.exe to disable logs. This technique was seen in several ransomware to disable the event logs to evade alerts and detections in compromised host.

• Type: TTP
• Product: Splunk Behavioral Analytics
• Datamodel: Endpoint_Processes
• Last Updated: 2021-06-15
• Author: Teoderick Contreras, Splunk
• ID: a4bdc944-cdd9-11eb-ac97-acde48001122

ATT&CK

ID	Technique	Tactic
T1070	Indicator Removal on Host	Defense Evasion

| T1070.001 | Clear Windows Event Logs | Defense Evasion |

Search

| from read_ssa_enriched_events() 
| where "Endpoint_Processes" IN(_datamodels) 
| eval timestamp=parse_long(ucast(map_get(input_event, "_time"), "string", null)), cmd_line=ucast(map_get(input_event, "process"), "string", null), process_name=ucast(map_get(input_event, "process_name"), "string", null), process_path=ucast(map_get(input_event, "process_path"), "string", null), parent_process_name=ucast(map_get(input_event, "parent_process_name"), "string", null), event_id=ucast(map_get(input_event, "event_id"), "string", null) 
| where cmd_line IS NOT NULL AND like(cmd_line, "% sl %") AND like(cmd_line, "%/e:false%") AND process_name="wevtutil.exe" 
| eval start_time=timestamp, end_time=timestamp, entities=mvappend(ucast(map_get(input_event, "dest_user_id"), "string", null), ucast(map_get(input_event, "dest_device_id"), "string", null)) 
| eval body=create_map(["event_id", event_id, "cmd_line", cmd_line, "process_name", process_name, "parent_process_name", parent_process_name, "process_path", process_path]) 
| into write_ssa_detected_events();

Associated Analytic Story

• Windows Log Manipulation
• Ransomware

How To Implement

You must be ingesting data that records process activity from your hosts to populate the Endpoint data model in the Processes node. You must also be ingesting logs with both the process name and command line from your endpoints. The command-line arguments are mapped to the "process" field in the Endpoint data model.

Required field

• _time
• dest_device_id
• process_name
• parent_process_name
• process_path
• dest_user_id
• process

Kill Chain Phase

• Exploitation

Known False Positives

network operator may disable audit event logs for debugging purposes.

RBA

Risk Score	Impact	Confidence	Message
63.0	70	90	A wevtutil process process_name with commandline cmd_line to disable event logs in host dest_device_id

Reference

• https://www.bleepingcomputer.com/news/security/new-ransom-x-ransomware-used-in-texas-txdot-cyberattack/

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

• https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1070.001/ssa_wevtutil/disable_evt.log

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