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Description

The following analytic identifies when a Windows Defender ASR rule disabled events. ASR is a feature of Windows Defender Exploit Guard that prevents actions and apps that are typically used by exploit-seeking malware to infect machines. ASR rules are applied to processes and applications. When a process or application attempts to perform an action that is blocked by an ASR rule, an event is generated. This detection searches for ASR rule disabled events that are generated when an ASR rule is disabled.

  • Type: TTP

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

  • Last Updated: 2023-11-27
  • Author: Michael Haag, Splunk
  • ID: 429d611b-3183-49a7-b235-fc4203c4e1cb

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1112 Modify Registry Defense Evasion
Kill Chain Phase
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


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`ms_defender` EventCode IN (5007) 
| rex field=New_Value "0x(?<New_Registry_Value>\\d+)$" 
| rex field=Old_Value "0x(?<Old_Registry_Value>\\d+)$" 
| rex field=New_Value "Rules\\\\(?<ASR_ID>[A-Fa-f0-9\\-]+)\\s*=" 
| lookup asr_rules ID AS ASR_ID OUTPUT ASR_Rule 
| eval New_Registry_Value=case(New_Registry_Value=="0", "Disabled", New_Registry_Value=="1", "Block", New_Registry_Value=="2", "Audit", New_Registry_Value=="6", "Warn") 
| eval Old_Registry_Value=case(Old_Registry_Value=="0", "Disabled", Old_Registry_Value=="1", "Block", Old_Registry_Value=="2", "Audit", Old_Registry_Value=="6", "Warn") 
| search New_Registry_Value="Disabled" 
| stats count min(_time) as firstTime max(_time) as lastTime by host, New_Value, Old_Value, Old_Registry_Value, New_Registry_Value, ASR_Rule 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)`
| rename host as dest 
| `windows_defender_asr_rule_disabled_filter`

Macros

The SPL above uses the following Macros:

:information_source: windows_defender_asr_rule_disabled_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Lookups

The SPL above uses the following Lookups:

Required fields

List of fields required to use this analytic.

  • host
  • New_Value
  • Old_Value
  • Old_Registry_Value
  • New_Registry_Value
  • ASR_Rule

How To Implement

The following analytic requires collection of Windows Defender Operational logs in either XML or multi-line. To collect, setup a new input for the Windows Defender Operational logs. In addition, it does require a lookup that maps the ID to ASR Rule name.

Known False Positives

False positives may occur if applications are typically disabling ASR rules in the environment. Monitor for changes to ASR rules to determine if this is a false positive.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
100.0 100 100 ASR rule disabled event, $ASR_Rule$, was triggered on $dest$.

:information_source: 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

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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