IMPORTANT: No additional bug fixes or documentation updates will be released for this version. For the latest information, see the current release documentation.

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Potential Shadow Credentials added to AD Object

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Potential Shadow Credentials added to AD Object

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Identify the modification of the msDS-KeyCredentialLink attribute in an Active Directory Computer or User Object. Attackers can abuse control over the object and create a key pair, append to raw public key in the attribute, and obtain persistent and stealthy access to the target user or computer object.

Rule type: query

Rule indices:

winlogbeat-*
logs-windows.*
logs-system.*

Severity: high

Risk score: 73

Runs every: 5 minutes

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

Elastic
Host
Windows
Threat Detection
Credential Access
Active Directory

Version: 1

Added (Elastic Stack release): 8.1.0

Rule authors: Elastic

Rule license: Elastic License v2

Potential false positives

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Modifications in the msDS-KeyCredentialLink attribute can be done legitimately by the Azure AD Connect synchronization account or the ADFS service account. These accounts can be added as Exceptions.

Investigation guide

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## Config

The 'Audit Directory Service Changes' logging policy must be configured for (Success, Failure).
Steps to implement the logging policy with Advanced Audit Configuration:

```
Computer Configuration >
Policies >
Windows Settings >
Security Settings >
Advanced Audit Policies Configuration >
Audit Policies >
DS Access >
Audit Directory Service Changes (Success,Failure)
```

The above policy does not cover User objects, so we need to set up an AuditRule using https://github.com/OTRF/Set-AuditRule.
As this specifies the msDS-KeyCredentialLink Attribute GUID, it is expected to be low noise.

```
Set-AuditRule -AdObjectPath 'AD:\CN=Users,DC=Domain,DC=com' -WellKnownSidType WorldSid -Rights WriteProperty -InheritanceFlags Children -AttributeGUID 5b47d60f-6090-40b2-9f37-2a4de88f3063 -AuditFlags Success
```

Rule query

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event.action:"Directory Service Changes" and event.code:"5136" and
winlog.event_data.AttributeLDAPDisplayName:"msDS-KeyCredentialLink"

Threat mapping

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Framework: MITRE ATT&CK^TM

Tactic:
- Name: Credential Access
- ID: TA0006
- Reference URL: https://attack.mitre.org/tactics/TA0006/
Technique:
- Name: Modify Authentication Process
- ID: T1556
- Reference URL: https://attack.mitre.org/techniques/T1556/

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