Cyber Heads Up: Unpacking “BadSuccessor” – A Critical Active Directory Vulnerability in Windows Server 2025

Akamai researchers have discovered a significant privilege escalation vulnerability in Windows Server 2025, dubbed “BadSuccessor.” This flaw targets the newly implemented delegated Managed Service Accounts (dMSAs) feature, which can be exploited by attackers to impersonate any Active Directory (AD) user, including domain administrators, without needing to change existing accounts or groups.

Key Details:

• Affected Feature: The vulnerability lies within the dMSAs in Windows Server 2025.
• Attack Mechanism: Attackers can create a dMSA with certain attributes, specifically msDS-ManagedAccountPrecededByLink and msDS-DelegatedMSAState, simulating the migration from an existing user account. This allows the Key Distribution Center (KDC) to grant the dMSA the privileges of the targeted account, leading to full impersonation.
• Prevalence: In a review of environments, 91% of non-administrative users held the permissions necessary to execute this attack.
• Microsoft’s Response: Microsoft has acknowledged the vulnerability but classified it as “moderate” in severity, indicating it does not necessitate immediate patching.

Impact:

The exploitation of the BadSuccessor vulnerability can result in total domain compromise, allowing attackers to:

• Access sensitive network data.
• Gain privileged entry to crucial systems and endpoints.
• Move laterally within the network undetected.

Significantly, the attack does not require any direct interaction with the targeted account, making it stealthy and challenging to identify.

Recommendations:

To mitigate risk until an official patch is available, organizations should take the following actions:

1. Audit Permissions: Restrict users with CreateChild permissions on Organizational Units (OUs), as these can be exploited to create dMSAs.
2. Monitor dMSA Creation: Implement monitoring for dMSA creation and changes to specific attributes, enabling the “Audit Directory Service Changes” logging policy.
3. Use Detection Tools: Utilize Akamai’s PowerShell script Get-BadSuccessorOUPermissions.ps1 to enumerate permissions relevant to creating dMSAs.
4. Restrict dMSA Usage: Limit the usage of dMSAs to essential scenarios and ensure only trusted administrators are permitted to create and manage them.
5. Stay Informed: Keep updated on Microsoft’s advisories regarding patches or additional guidance concerning this vulnerability.

Conclusion:

The BadSuccessor vulnerability accentuates that new features within robust systems like Active Directory can inadvertently introduce serious security risks. Organizations must not only focus on implementing technical measures but also reassess their management of permissions, account creation processes, and directory monitoring strategies.

For further reading, see:

1. Akamai Security Research article on abusing dMSA for privilege escalation: Read Here
2. Ori David’s LinkedIn post discussing the discovery: LinkedIn Post

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