Detection: Windows AD Replication Request Initiated from Unsanctioned Location

Description

The following analytic identifies unauthorized Active Directory replication requests initiated from non-domain controller locations. It leverages EventCode 4662 to detect when a computer account with replication permissions creates a handle to domainDNS, filtering out known domain controller IP addresses. This activity is significant as it may indicate a DCSync attack, where an attacker with privileged access can request password hashes for any or all users within the domain. If confirmed malicious, this could lead to unauthorized access to sensitive information and potential full domain compromise.

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 (SubjectUserSid="NT AUT*" OR SubjectUserSid="S-1-5-18" OR SubjectDomainName="Window Manager" OR SubjectUserName="*$") 
2| stats min(_time) as attack_time, count by SubjectDomainName, SubjectUserName, Computer, Logon_ID, ObjectName, ObjectServer, ObjectType, OperationType, status 
3| rename SubjectDomainName as Target_Domain, SubjectUserName as user, Logon_ID as TargetLogonId 
4| appendpipe [
5| map search="search `wineventlog_security` EventCode=4624 TargetLogonId=$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| search NOT src_category="domain_controller" 
9| `windows_ad_replication_request_initiated_from_unsanctioned_location_filter`

Data Source

Name	Platform	Sourcetype	Source
Windows Event Log Security 4624	Windows	'xmlwineventlog'	'XmlWinEventLog:Security'
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 Assets and Identities will also need to be configured, with the category of domain_controller added for domain controllers.

Known False Positives

Genuine DC promotion may trigger this alert.

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: 6