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Description

This detection identifies an Active Directory access-control list (ACL) modification event, which applies permissions that deny the ability to enumerate permissions of the object.

  • Type: TTP

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

  • Last Updated: 2023-11-21
  • Author: Dean Luxton
  • ID: 8e897153-2ebd-4cb2-85d3-09ad57db2fb7

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1484 Domain or Tenant Policy Modification Defense Evasion, Privilege Escalation
T1222 File and Directory Permissions Modification Defense Evasion
T1222.001 Windows File and Directory Permissions Modification Defense Evasion
Kill Chain Phase
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 10
CVE 


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`wineventlog_security` EventCode=5136 
| 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<aceInheritedTypeGuid>.*?);(?P<aceSid>.*?)$"  
| 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 as aceType 
| 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 values(aceType) as aceType values(aceFlags) as aceFlags values(aceControlAccessRights) as aceControlAccessRights values(aceAccessRights) as aceAccessRights values(new_ace) as new_ace values(aceInheritedTypeGuid) as aceInheritedTypeGuid by _time ObjectClass ObjectDN src_user SubjectLogonId user OpCorrelationID 
| eval aceControlAccessRights=if(mvcount(aceControlAccessRights)=1 AND aceControlAccessRights="","All rights",'aceControlAccessRights') 
| search aceType IN ("Access denied",D) AND aceAccessRights IN ("Full control","Read permissions",RC) 
| `windows_ad_dangerous_deny_acl_modification_filter`

Macros

The SPL above uses the following Macros:

:information_source: windows_ad_dangerous_deny_acl_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.

  • _time
  • OperationType
  • ObjectDN
  • OpCorrelationID
  • src_user
  • AttributeLDAPDisplayName
  • AttributeValue
  • ObjectClass
  • SubjectLogonId
  • DSName

How To Implement

Ensure you are ingesting Active Directory audit logs - specifically event 5136. See lantern article in references for further on how to onboard AD audit data. Ensure the wineventlog_security macro is configured with the correct indexes and include lookups for SID resolution if evt_resolve_ad_obj is set to 0.

Known False Positives

None.

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
100.0 100 100 $src_user$ has added ACL rights to deny $user$ $aceControlAccessRights$ $aceAccessRights$ to $ObjectDN$

: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

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