:warning: THIS IS A EXPERIMENTAL DETECTION

This detection has been marked experimental by the Splunk Threat Research team. This means we have not been able to test, simulate, or build datasets for this detection. Use at your own risk. This analytic is NOT supported.

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Description

The following analytic detects the addition of the permissions necessary to perform a DCSync attack. In order to replicate AD objects, the initiating user or computer must have the following permissions on the domain. - DS-Replication-Get-Changes - DS-Replication-Get-Changes-All Certain Sync operations may require the additional permission of DS-Replication-Get-Changes-In-Filtered-Set. By default, adding DCSync permissions via the Powerview Add-ObjectACL operation adds all 3. This alert identifies where this trifecta has been met, and also where just the base level requirements have been met.

  • Type: TTP
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Change
  • Last Updated: 2022-11-18
  • Author: Dean Luxton
  • ID: 8c372853-f459-4995-afdc-280c114d33ab

Annotations

ATT&CK

ATT&CK

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


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`wineventlog_security`  
| rex field=AttributeValue max_match=10000 \"OA;;CR;89e95b76-444d-4c62-991a-0facbeda640c;;(?P<DSRGetChangesFiltered_user_sid>S-1-[0-59]-\d{2}-\d{8,10}-\d{8,10}-\d{8,10}-[1-9]\d{3})\)\"
| table _time dest src_user DSRGetChanges_user_sid DSRGetChangesAll_user_sid DSRGetChangesFiltered_user_sid
| mvexpand DSRGetChanges_user_sid
| eval minDCSyncPermissions=if(DSRGetChanges_user_sid=DSRGetChangesAll_user_sid,\"true\",\"false\"), fullSet=if(DSRGetChanges_user_sid=DSRGetChangesAll_user_sid AND DSRGetChanges_user_sid=DSRGetChangesFiltered_user_sid,\"true\",\"false\")
| where minDCSyncPermissions=\"true\" 
| lookup identity_lookup_expanded  objectSid as DSRGetChanges_user_sid OUTPUT sAMAccountName as user 
| rename DSRGetChanges_user_sid as userSid 
| stats min(_time) as _time values(user) as user by dest src_user userSid minDCSyncPermissions fullSet
| `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.

Required fields

List of fields required to use this analytic.

  • _time
  • dest
  • 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: 1