ID | Technique | Tactic |
---|---|---|
T1562.001 | Disable or Modify Tools | Defense Evasion |
T1562 | Impair Defenses | Defense Evasion |
Detection: Disable AMSI Through Registry
Description
The following analytic detects modifications to the Windows registry that disable the Antimalware Scan Interface (AMSI) by setting the "AmsiEnable" value to "0x00000000". This detection leverages data from the Endpoint.Registry data model, specifically monitoring changes to the registry path "*\SOFTWARE\Microsoft\Windows Script\Settings\AmsiEnable". Disabling AMSI is significant as it is a common technique used by ransomware, Remote Access Trojans (RATs), and Advanced Persistent Threats (APTs) to evade detection and impair defenses. If confirmed malicious, this activity could allow attackers to execute payloads with minimal alerts, leading to potential system compromise and data exfiltration.
Search
1
2| tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Registry WHERE (Registry.registry_path= "*\\SOFTWARE\\Microsoft\\Windows Script\\Settings\\AmsiEnable" Registry.registry_value_data = "0x00000000") BY _time span=1h Registry.registry_path Registry.registry_key_name Registry.registry_value_name Registry.registry_value_data Registry.process_guid Registry.dest Registry.user
3| `drop_dm_object_name(Registry)`
4| where isnotnull(registry_value_data)
5| `security_content_ctime(firstTime)`
6| `security_content_ctime(lastTime)`
7| `disable_amsi_through_registry_filter`
Data Source
Name | Platform | Sourcetype | Source |
---|---|---|---|
Sysmon EventID 12 | Windows | 'xmlwineventlog' |
'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational' |
Sysmon EventID 13 | Windows | 'xmlwineventlog' |
'XmlWinEventLog:Microsoft-Windows-Sysmon/Operational' |
Macros Used
Name | Value |
---|---|
security_content_ctime | convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$) |
disable_amsi_through_registry_filter | search * |
disable_amsi_through_registry_filter
is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
Annotations
Default Configuration
This detection is configured by default in Splunk Enterprise Security to run with the following settings:
Setting | Value |
---|---|
Disabled | true |
Cron Schedule | 0 * * * * |
Earliest Time | -70m@m |
Latest Time | -10m@m |
Schedule Window | auto |
Creates Notable | Yes |
Rule Title | %name% |
Rule Description | %description% |
Notable Event Fields | user, dest |
Creates Risk Event | True |
Implementation
To successfully implement this search, you need to be ingesting logs with the registry value name, registry path, and registry value data from your endpoints. If you are using Sysmon, you must have at least version 2.0 of the offical Sysmon TA. https://splunkbase.splunk.com/app/5709
Known False Positives
network operator may disable this feature of windows but not so common.
Associated Analytic Story
Risk Based Analytics (RBA)
Risk Message | Risk Score | Impact | Confidence |
---|---|---|---|
Disable AMSI Through Registry on $dest$ | 25 | 50 | 50 |
References
Detection Testing
Test Type | Status | Dataset | Source | Sourcetype |
---|---|---|---|---|
Validation | ✅ Passing | N/A | N/A | N/A |
Unit | ✅ Passing | Dataset | XmlWinEventLog:Microsoft-Windows-Sysmon/Operational |
XmlWinEventLog |
Integration | ✅ Passing | Dataset | XmlWinEventLog:Microsoft-Windows-Sysmon/Operational |
XmlWinEventLog |
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: 6