| ID | Technique | Tactic |
|---|---|---|
| T1222.001 | Windows Permissions | Defense Impairment |
| T1484 | Domain or Tenant Policy Modification | Defense Impairment |
Detection: Windows AD Dangerous Deny ACL Modification
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.
Search
1`wineventlog_security` EventCode=5136
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 values(dest) as dest 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 msad_guid_lookup guid as aceObjectGuid OUTPUT displayName as ControlAccessRights
11| lookup ace_access_rights_lookup access_rights_string as AccessRights OUTPUT access_rights_value
12| lookup ace_type_lookup ace_type_string as aceType OUTPUT ace_type_value as aceType
13| lookup ace_flag_lookup flag_string as aceFlags OUTPUT flag_value as ace_flag_value ``` 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), 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)
18| 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
19| eval aceControlAccessRights=if(mvcount(aceControlAccessRights)=1 AND aceControlAccessRights="","All rights",'aceControlAccessRights')
20| search aceType IN ("Access denied",D) AND aceAccessRights IN ("Full control","Read permissions",RC)
21| `windows_ad_dangerous_deny_acl_modification_filter`
Data Source
| Name | Platform | Sourcetype | Source |
|---|---|---|---|
| Windows Event Log Security 5136 |  Windows |
'XmlWinEventLog' |
'XmlWinEventLog:Security' |
Macros Used
| Name | Value |
|---|---|
| wineventlog_security | eventtype="wineventlog_security" OR Channel="security" OR source="XmlWinEventLog:Security" OR source="WinEventLog:Security" |
| windows_ad_dangerous_deny_acl_modification_filter | search * |
windows_ad_dangerous_deny_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
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 Finding (Notable) | Yes |
| Rule Title | %name% |
| Rule Description | %description% |
| Notable Event Fields | user, dest |
| Creates Intermediate Finding (Risk Event) | Yes |
TTP detections generate a Finding (Notable) and may generate Intermediate Findings (Risk Events) for associated entities.
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
No false positives have been identified at this time.
Associated Analytic Story
Finding
| Title | Entity Field | Entity Type | Risk Score |
|---|---|---|---|
| $src_user$ has added ACL rights to deny $user$ $aceControlAccessRights$ $aceAccessRights$ to $ObjectDN$ | src_user | user | 50 |
Intermediate Findings
| Message | Entity Field | Entity Type | Risk Score |
|---|---|---|---|
| $src_user$ has added ACL rights to deny $user$ $aceControlAccessRights$ $aceAccessRights$ to $ObjectDN$ | user | user | 50 |
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: 10