msDS-ManagedAccountPrecededByLink Attribute Modified

SIGMA detection rule by Swachchhanda Shrawan Poudel (Nextron Systems) · NOASSERTION

Detects modifications to the msDS-ManagedAccountPrecededByLink attribute, which may indicate an attempted or successful abuse of the BaD-Successor msDS-DelegatedManagedServiceAccount (DMSA) vulnerability. The DMSA is a new object class introduced in Windows Server 2025 that allows administrators to delegate the management of service accounts to other users or groups. Changes to this attribute by suspicious accounts or outside of normal administrative workflows are a strong signal of an attempted or successful abuse. If it is indeed modified by an account that is not typically responsible for such changes, it could indicate an attempt to exploit the BaD-Successor vulnerability for privilege escalation within the Windows Server 2025 Active Directory environment.

title: msDS-ManagedAccountPrecededByLink Attribute Modified
id: 6c9eb492-e477-4df9-b0f4-571fc9db29cd
related:
    - id: 9b111d8e-92e0-4153-88bc-daefc1333aba
      type: similar
status: experimental
description: |
    Detects modifications to the msDS-ManagedAccountPrecededByLink attribute, which may indicate an attempted or successful abuse of the BaD-Successor msDS-DelegatedManagedServiceAccount (DMSA) vulnerability.
    The DMSA is a new object class introduced in Windows Server 2025 that allows administrators to delegate the management of service accounts to other users or groups.
    Changes to this attribute by suspicious accounts or outside of normal administrative workflows are a strong signal of an attempted or successful abuse.
    If it is indeed modified by an account that is not typically responsible for such changes, it could indicate an attempt to exploit the BaD-Successor vulnerability for privilege escalation within the Windows Server 2025 Active Directory environment.
references:
    - https://www.akamai.com/blog/security-research/abusing-bad-successor-for-privilege-escalation-in-active-directory
author: Swachchhanda Shrawan Poudel (Nextron Systems)
date: 2025-05-24
tags:
    - attack.privilege-escalation
    - attack.initial-access
    - attack.persistence
    - attack.stealth
    - attack.t1078.002
    - attack.t1098
logsource:
    product: windows
    service: security
    definition: 'Requirements: Audit Policy : Account Management > Audit User Account Management, Group Policy : Computer Configuration\Windows Settings\Security Settings\Advanced Audit Policy Configuration\Audit Policies\Account Management\Audit User Account Management, DS Access > Audit Directory Service Changes, Group Policy : Computer Configuration\Windows Settings\Security Settings\Advanced Audit Policy Configuration\Audit Policies\DS Access\Audit Directory Service Changes'
detection:
    selection:
        EventID: 5136
        ObjectClass: 'msDS-DelegatedManagedServiceAccount'
        AttributeLDAPDisplayName: 'msDS-ManagedAccountPrecededByLink'
    filter_main_legitimate_accounts:
        # Exclude modifications made by the system or legitimate administrative accounts
        - SubjectAccountName: 'SYSTEM'
        - SubjectAccountName|expand: '%Administrators%' # Add all members of the Administrators group to this placeholder
    condition: selection and not 1 of filter_main_*
falsepositives:
    - Unknown
# The level is set to medium because while this is a significant event, it may not always indicate malicious activity. It requires further investigation to determine the context and intent behind the modification.
level: medium

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