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Description

The following analytic detects modifications to Windows Defender Attack Surface Reduction (ASR) registry settings. It leverages Windows Defender Operational logs, specifically EventCode 5007, to identify changes in ASR rules. This activity is significant because ASR rules are designed to block actions commonly used by malware to exploit systems. Unauthorized modifications to these settings could indicate an attempt to weaken system defenses. If confirmed malicious, this could allow an attacker to bypass security measures, leading to potential system compromise and data breaches.

  • Type: Hunting

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

  • Last Updated: 2024-08-14
  • Author: Michael Haag, Splunk
  • ID: 6a1b6cbe-6612-44c3-92b9-1a1bd77412eb

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1112 Modify Registry Defense Evasion
Kill Chain Phase
  • Exploitation
NIST
  • DE.AE
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*=" 
| 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") 
| stats count min(_time) as firstTime max(_time) as lastTime by host, New_Value, Old_Value, Old_Registry_Value, New_Registry_Value, ASR_ID 
| lookup asr_rules ID AS ASR_ID OUTPUT ASR_Rule 
| `security_content_ctime(firstTime)`
| rename host as dest 
| `security_content_ctime(lastTime)` 
| `windows_defender_asr_registry_modification_filter`

Macros

The SPL above uses the following Macros:

:information_source: windows_defender_asr_registry_modification_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 are expected from legitimate applications generating events that are similar to those generated by malicious activity. For example, Event ID 5007 is generated when a process attempts to modify a registry key that is related to ASR rules. This can be triggered by legitimate applications that attempt to modify registry keys that are not blocked by ASR rules.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
50.0 50 100 ASR registry modification 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

source | version: 3