Windows AD Domain Replication ACL Addition
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.
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: 2024-05-16
- Author: Dean Luxton
- ID: 8c372853-f459-4995-afdc-280c114d33ab
Annotations
ATT&CK
Kill Chain Phase
- Exploitation
NIST
- DE.CM
CIS20
- CIS 10
CVE
Search
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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:
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 |
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
- https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-adts/1522b774-6464-41a3-87a5-1e5633c3fbbb
- https://github.com/SigmaHQ/sigma/blob/29a5c62784faf986dc03952ae3e90e3df3294284/rules/windows/builtin/security/win_security_account_backdoor_dcsync_rights.yml
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: 2