Detection: Windows AD Replication Request Initiated by User Account

Description

The following analytic detects a user account initiating an Active Directory replication request, indicative of a DCSync attack. It leverages EventCode 4662 from the Windows Security Event Log, focusing on specific object types and replication permissions. This activity is significant because it can allow an attacker with sufficient privileges to request password hashes for any or all users within the domain. If confirmed malicious, this could lead to unauthorized access, privilege escalation, and potential compromise of the entire domain.

Search

1`wineventlog_security` EventCode=4662 ObjectType IN ("%{19195a5b-6da0-11d0-afd3-00c04fd930c9}", "domainDNS") AND Properties IN ("*Replicating Directory Changes All*", "*{1131f6ad-9c07-11d1-f79f-00c04fc2dcd2}*", "*{9923a32a-3607-11d2-b9be-0000f87a36b2}*","*{1131f6ac-9c07-11d1-f79f-00c04fc2dcd2}*") AND AccessMask="0x100" AND NOT (SubjectUserSid="NT AUT*" OR SubjectUserSid="S-1-5-18" OR SubjectDomainName="Window Manager" OR SubjectUserName="*$") 
2| stats min(_time) as _time, count by SubjectDomainName, SubjectUserName, Computer, Logon_ID, ObjectName, ObjectServer, ObjectType, OperationType, status 
3| rename SubjectDomainName as Target_Domain, SubjectUserName as user, Logon_ID as TargetLogonId, _time as attack_time 
4| appendpipe [
5| map search="search `wineventlog_security` EventCode=4624 TargetLogonId=$TargetLogonId$"] 
6| table attack_time, AuthenticationPackageName, LogonProcessName, LogonType, TargetUserSid, Target_Domain, user, Computer, TargetLogonId, status, src_ip, src_category, ObjectName, ObjectServer, ObjectType, OperationType 
7| stats min(attack_time) as _time values(TargetUserSid) as TargetUserSid, values(Target_Domain) as Target_Domain, values(user) as user, values(Computer) as Computer, values(status) as status, values(src_category) as src_category, values(src_ip) as src_ip by TargetLogonId 
8| `windows_ad_replication_request_initiated_by_user_account_filter`

Data Source

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

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Implementation

To successfully implement this search, you need to be ingesting eventcode 4662. The Advanced Security Audit policy settings Audit Directory Services Access within DS Access needs to be enabled, as well as the following SACLs applied to the domain root and all descendant objects. The principals everybody, Domain Computers, and Domain Controllers auditing the permissions Replicating Directory Changes, Replicating Directory Changes All, and Replicating Directory Changes In Filtered Set

Known False Positives

Azure AD Connect syncing operations.

Associated Analytic Story

• Compromised Windows Host

• Credential Dumping

• Sneaky Active Directory Persistence Tricks

Risk Based Analytics (RBA)

References

• https://adsecurity.org/?p=1729

• https://www.linkedin.com/pulse/mimikatz-dcsync-event-log-detections-john-dwyer

• https://github.com/SigmaHQ/sigma/blob/0.22-699-g29a5c6278/rules/windows/builtin/security/win_security_dcsync.yml

Detection Testing

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: 5