Detection: Windows AD Dangerous Group ACL Modification

Updated Date: 2023-11-13 ID: 59b0fc85-7a0d-4585-97ec-06a382801990 Author: Dean Luxton Type: TTP Product: Splunk Enterprise Security

Description

This detection monitors the addition of the following ACLs to an Active Directory group object: "Full control", "All extended rights", "All validated writes", "Create all child objects", "Delete all child objects", "Delete subtree", "Delete", "Modify permissions", "Modify owner", and "Write all properties". Such modifications can indicate potential privilege escalation or malicious activity. Immediate investigation is recommended upon alert.

 1`wineventlog_security` EventCode=5136 ObjectClass=group 
 2| 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  
 3| rex field=old_value max_match=10000 "\((?P<old_values>.*?)\)"  
 4| rex field=new_value max_match=10000 "\((?P<new_ace>.*?)\)"  
 5| mvexpand new_ace  
 6| where NOT new_ace IN (old_values)  
 7| rex field=new_ace "(?P<aceType>.*?);(?P<aceFlags>.*?);(?P<aceAccessRights>.*?);(?P<aceObjectGuid>.*?);(?P<aceInheritedTypeGuid>.*?);(?P<aceSid>.*?)$"  
 8| rex max_match=100 field=aceAccessRights "(?P<AccessRights>[A-Z]{2})"  
 9| rex max_match=100 field=aceFlags "(?P<aceFlags>[A-Z]{2})"  
10| lookup ace_type_lookup ace_type_string as aceType OUTPUT ace_type_value as aceType 
11| lookup ace_flag_lookup flag_string as aceFlags OUTPUT flag_value as ace_flag_value 
12| lookup ace_access_rights_lookup access_rights_string as AccessRights OUTPUT access_rights_value  
13| lookup msad_guid_lookup guid as aceObjectGuid OUTPUT displayName as ControlAccessRights ``` Optional SID resolution lookups 
14| lookup identity_lookup_expanded objectSid as aceSid OUTPUT downLevelDomainName as user  
15| lookup admon_groups_def objectSid as aceSid OUTPUT cn as group ``` 
16| lookup builtin_groups_lookup builtin_group_string  as aceSid OUTPUT builtin_group_name as builtin_group 
17| eval aceType=coalesce(ace_type_value,aceType), aceInheritance=coalesce(ace_flag_value,"This object only"), aceAccessRights=if(aceAccessRights="CCDCLCSWRPWPDTLOCRSDRCWDWO","Full control",coalesce(access_rights_value,AccessRights)), aceControlAccessRights=if((ControlAccessRights="Write member" OR aceObjectGuid="bf9679c0-0de6-11d0-a285-00aa003049e2") AND (aceAccessRights="All validated writes" OR AccessRights="SW"),"Add/remove self as member",coalesce(ControlAccessRights,aceObjectGuid)), user=coalesce(user, group, builtin_group, aceSid) 
18| stats values(aceType) as aceType values(aceInheritance) as aceInheritance 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 
19| eval aceControlAccessRights=if(mvcount(aceControlAccessRights)=1 AND aceControlAccessRights="","All rights",'aceControlAccessRights') 
20| search NOT aceType IN ("*denied*","D","OD","XD") AND aceAccessRights IN ("Full control","All extended rights","All validated writes","Create all child objects","Delete all child objects","Delete subtree","Delete","Modify permissions","Modify owner","Write all properties",CC,CR,DC,DT,SD,SW,WD,WO,WP) 
21| `windows_ad_dangerous_group_acl_modification_filter`

Data Source

Name Platform Sourcetype Source Supported App
N/A N/A N/A N/A N/A

Macros Used

Name Value
wineventlog_security eventtype=wineventlog_security OR Channel=security OR source=XmlWinEventLog:Security
windows_ad_dangerous_group_acl_modification_filter search *
windows_ad_dangerous_group_acl_modification_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
T1484 Domain or Tenant Policy Modification Defense Evasion
T1222 File and Directory Permissions Modification Privilege Escalation
T1222.001 Windows File and Directory Permissions Modification Defense Evasion
KillChainPhase.EXPLOITAITON
NistCategory.DE_CM
Cis18Value.CIS_10
Wizard Spider

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 Notable Yes
Rule Title %name%
Rule Description %description%
Notable Event Fields user, dest
Creates Risk Event True
This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

Implementation

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

Unknown

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message Risk Score Impact Confidence
$src_user$ has added ACL rights to grant $user$ $aceControlAccessRights$ $aceAccessRights$ to group $ObjectDN$ 100 100 100
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: 1