Detection: Windows AD Abnormal Object Access Activity

Updated Date: 2024-09-30 ID: 71b289db-5f2c-4c43-8256-8bf26ae7324a Author: Steven Dick Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic identifies a statistically significant increase in access to Active Directory objects, which may indicate attacker enumeration. It leverages Windows Security Event Code 4662 to monitor and analyze access patterns, comparing them against historical averages to detect anomalies. This activity is significant for a SOC because abnormal access to AD objects can be an early indicator of reconnaissance efforts by an attacker. If confirmed malicious, this behavior could lead to unauthorized access, privilege escalation, or further compromise of the Active Directory environment.

Search

1`wineventlog_security` EventCode=4662 
2| stats min(_time) AS firstTime, max(_time) AS lastTime, dc(ObjectName) AS ObjectName_count, values(ObjectType) AS ObjectType, latest(Computer) AS dest count BY SubjectUserName 
3| eventstats avg(ObjectName_count) AS average stdev(ObjectName_count) AS standarddev 
4| eval limit = round((average+(standarddev*3)),0), user = SubjectUserName 
5| where ObjectName_count > limit 
6| `security_content_ctime(firstTime)` 
7| `security_content_ctime(lastTime)`
8| `windows_ad_abnormal_object_access_activity_filter`

Data Source

Name	Platform	Sourcetype	Source
Windows Event Log Security 4662	Windows	`'xmlwineventlog'`	`'XmlWinEventLog:Security'`

Macros Used

Name	Value
security_content_ctime	`convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)`
windows_ad_abnormal_object_access_activity_filter	`search *`

windows_ad_abnormal_object_access_activity_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK

+ Kill Chain Phases

+ NIST

+ CIS

- Threat Actors

ID	Technique	Tactic
T1087	Account Discovery	Discovery
T1087.002	Domain Account	Discovery

KillChainPhase.EXPLOITAITON

NistCategory.DE_AE

Cis18Value.CIS_10

Aquatic Panda

FIN13

APT41

BRONZE BUTLER

Chimera

Dragonfly

FIN13

FIN6

Fox Kitten

INC Ransom

Ke3chang

LAPSUS$

MuddyWater

OilRig

Poseidon Group

RedCurl

Sandworm Team

Scattered Spider

ToddyCat

Turla

Volt Typhoon

Wizard Spider

menuPass

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 Risk Event	True

This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

Enable Audit Directory Service Access via GPO and collect event code 4662. The required SACLs need to be created for the relevant objects. Be aware Splunk filters this event by default on the Windows TA. Recommend pre-filtering any known service accounts that frequently query AD to make detection more accurate. Setting wide search window of 48~72hr may smooth out misfires.

Known False Positives

Service accounts or applications that routinely query Active Directory for information.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
The account $user$ accessed an abnormal amount ($ObjectName_count$) of [$ObjectType$] AD object(s) between $firstTime$ and $lastTime$.	25	50	50

The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`XmlWinEventLog:Security`	`XmlWinEventLog`
Integration	✅ Passing	Dataset	`XmlWinEventLog:Security`	`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: 3