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Description

The following analytic detects the addition of permissions required for a DCSync attack, specifically DS-Replication-Get-Changes, DS-Replication-Get-Changes-All, and DS-Replication-Get-Changes-In-Filtered-Set. It leverages EventCode 5136 from the Windows Security Event Log to identify when these permissions are granted. This activity is significant because it indicates potential preparation for a DCSync attack, which can be used to replicate AD objects and exfiltrate sensitive data. If confirmed malicious, an attacker could gain extensive access to Active Directory, leading to severe data breaches and privilege escalation.

  • Type: TTP
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Change
  • Last Updated: 2024-08-08
  • Author: Dean Luxton
  • ID: 8c372853-f459-4995-afdc-280c114d33ab

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1484 Domain or Tenant Policy Modification Defense Evasion, Privilege Escalation
Kill Chain Phase
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


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`wineventlog_security` EventCode=5136 ObjectClass=domainDNS  
| stats min(_time) as _time values(eval(if(OperationType=="%%14675",AttributeValue,null))) as old_value values(eval(if(OperationType=="%%14674",AttributeValue,null))) as new_value values(OperationType) as OperationType by ObjectClass ObjectDN OpCorrelationID src_user SubjectLogonId  
| rex field=old_value max_match=10000 "\((?P<old_values>.*?)\)"  
| rex field=new_value max_match=10000 "\((?P<new_ace>.*?)\)"  
| mvexpand new_ace 
| where NOT new_ace IN (old_values)  
| rex field=new_ace "(?P<aceType>.*?);(?P<aceFlags>.*?);(?P<aceAccessRights>.*?);(?P<aceObjectGuid>.*?);;(?P<aceSid>.*?)$" 
| search aceObjectGuid IN ("1131f6aa-9c07-11d1-f79f-00c04fc2dcd2","1131f6ad-9c07-11d1-f79f-00c04fc2dcd2","89e95b76-444d-4c62-991a-0facbeda640c") 
| rex max_match=100 field=aceAccessRights "(?P<AccessRights>[A-Z]{2})"  
| rex max_match=100 field=aceFlags "(?P<aceFlags>[A-Z]{2})"  
| lookup msad_guid_lookup guid as aceObjectGuid OUTPUT displayName as ControlAccessRights 
| lookup ace_access_rights_lookup access_rights_string as AccessRights OUTPUT access_rights_value  
| lookup ace_type_lookup ace_type_string as aceType OUTPUT ace_type_value  
| lookup ace_flag_lookup flag_string as aceFlags OUTPUT flag_value as ace_flag_value ``` Optional SID resolution lookups 
| lookup identity_lookup_expanded objectSid as aceSid OUTPUT downLevelDomainName as user  
| lookup admon_groups_def objectSid as aceSid OUTPUT cn as group ``` 
| lookup builtin_groups_lookup builtin_group_string  as aceSid OUTPUT builtin_group_name as builtin_group 
| eval aceType=coalesce(ace_type_value,aceType), aceFlags=coalesce(ace_flag_value,"This object only"), aceAccessRights=if(aceAccessRights="CCDCLCSWRPWPDTLOCRSDRCWDWO","Full control",coalesce(access_rights_value,AccessRights)), aceControlAccessRights=coalesce(ControlAccessRights,aceObjectGuid), user=coalesce(user, group, builtin_group, aceSid) 
| stats min(_time) as _time values(aceType) as aceType values(aceFlags) as aceFlags(inheritance) values(aceControlAccessRights) as aceControlAccessRights values(aceAccessRights) as aceAccessRights values(new_ace) as new_ace values(SubjectLogonId) as SubjectLogonId by ObjectClass ObjectDN src_user user 
| search (aceControlAccessRights="DS-Replication-Get-Changes" AND aceControlAccessRights="DS-Replication-Get-Changes-All") OR (aceControlAccessRights="1131f6aa-9c07-11d1-f79f-00c04fc2dcd2" AND aceControlAccessRights="1131f6ad-9c07-11d1-f79f-00c04fc2dcd2") 
| `windows_ad_domain_replication_acl_addition_filter`

Macros

The SPL above uses the following Macros:

:information_source: windows_ad_domain_replication_acl_addition_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.

  • _time
  • OperationType
  • src_user
  • AttributeLDAPDisplayName
  • AttributeValue
  • ObjectClass

How To Implement

To successfully implement this search, you need to be ingesting the eventcode 5136. The Advanced Security Audit policy setting Audit Directory Services Changes within DS Access needs to be enabled, alongside a SACL for everybody to Write All Properties applied to the domain root and all descendant objects. Once the necessary logging has been enabled, enumerate the domain policy to verify if existing accounts with access need to be whitelisted, or revoked. Assets and Identities is also leveraged to automatically translate the objectSid into username. Ensure your identities lookup is configured with the sAMAccountName and objectSid of all AD user and computer objects.

Known False Positives

When there is a change to nTSecurityDescriptor, Windows logs the entire ACL with the newly added components. If existing accounts are present with this permission, they will raise an alert each time the nTSecurityDescriptor is updated unless whitelisted.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
80.0 100 80 $src_user$ has granted $user$ permission to replicate AD objects

: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: 4