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Detection rules › Sigma

Possible Shadow Credentials Added

Status
test
Severity
high
Log source
product windows, service security
Author
Nasreddine Bencherchali (Nextron Systems), Elastic (idea)
Source
github.com/SigmaHQ/sigma

Detects possible addition of shadow credentials to an active directory object.

MITRE ATT&CK coverage

TacticTechniques
PersistenceT1556 Modify Authentication Process
Defense ImpairmentT1556 Modify Authentication Process
Credential AccessT1556 Modify Authentication Process

Event coverage

ProviderEventTitle
Security-AuditingEvent ID 5136A directory service object was modified.

Rule body yaml

title: Possible Shadow Credentials Added
id: f598ea0c-c25a-4f72-a219-50c44411c791
status: test
description: Detects possible addition of shadow credentials to an active directory object.
references:
    - https://www.elastic.co/guide/en/security/8.4/potential-shadow-credentials-added-to-ad-object.html
    - https://cyberstoph.org/posts/2022/03/detecting-shadow-credentials/
    - https://twitter.com/SBousseaden/status/1581300963650187264?
author: Nasreddine Bencherchali (Nextron Systems), Elastic (idea)
date: 2022-10-17
tags:
    - attack.persistence
    - attack.credential-access
    - attack.defense-impairment
    - attack.t1556
logsource:
    product: windows
    service: security
    definition: The "Audit Directory Service Changes" logging policy must be configured in order to receive events. Audit events are generated only for objects with configured system access control lists (SACLs). Audit events are generated only for objects with configured system access control lists (SACLs) and only when accessed in a manner that matches their SACL settings. This policy covers the following events ids - 5136, 5137, 5138, 5139, 5141. Note that the default policy does not cover User objects. For that a custom AuditRule need to be setup (See https://github.com/OTRF/Set-AuditRule)
detection:
    selection:
        EventID: 5136
        AttributeLDAPDisplayName: 'msDS-KeyCredentialLink'
        # If you experience a lot of FP you could uncomment the selection below
        # There could be other cases for other tooling add them accordingly
        # AttributeValue|contains: 'B:828'
        # OperationType: '%%14674' # Value Added
    # As stated in the FP sections it's better to filter out the expected accounts that perform this operation to tighten the logic
    # Uncomment the filter below and add the account name (or any other specific field) accordingly
    # Don't forget to add it to the condition section below
    # filter:
        # SubjectUserName: "%name%"
    condition: selection
falsepositives:
    - 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. (From elastic FP section)
level: high

Stages and Predicates

Stage 0: condition

selection

Stage 1: selection

selection:
    EventID: 5136
    AttributeLDAPDisplayName: 'msDS-KeyCredentialLink'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
AttributeLDAPDisplayNameeq
  • msDS-KeyCredentialLink corpus 2 (sigma 1, elastic 1)