Abusing Active Directory ACLs/ACEs

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Overview

Delegated Managed Service Accounts (dMSAs) are a brand‑new AD principal type introduced with Windows Server 2025. They are designed to replace legacy service accounts by allowing a one‑click “migration” that automatically copies the old account’s Service Principal Names (SPNs), group memberships, delegation settings, and even cryptographic keys into the new dMSA, giving applications a seamless cut‑over and eliminating Kerberoasting risk.

Akamai researchers found that a single attribute — msDS‑ManagedAccountPrecededByLink — tells the KDC which legacy account a dMSA “succeeds”. If an attacker can write that attribute (and toggle msDS‑DelegatedMSAState → 2), the KDC will happily build a PAC that inherits every SID of the chosen victim, effectively allowing the dMSA to impersonate any user, including Domain Admins.

What exactly is a dMSA?

• Built on top of gMSA technology but stored as the new AD class msDS‑DelegatedManagedServiceAccount.
• Supports an opt‑in migration: calling Start‑ADServiceAccountMigration links the dMSA to the legacy account, grants the legacy account write access to msDS‑GroupMSAMembership, and flips msDS‑DelegatedMSAState = 1.
• After Complete‑ADServiceAccountMigration, the superseded account is disabled and the dMSA becomes fully functional; any host that previously used the legacy account is automatically authorised to pull the dMSA’s password.
• During authentication, the KDC embeds a KERB‑SUPERSEDED‑BY‑USER hint so Windows 11/24H2 clients transparently retry with the dMSA.

## Requirements to attack

1. At least one Windows Server 2025 DC so that the dMSA LDAP class and KDC logic exist.
2. Any object‑creation or attribute‑write rights on an OU (any OU) – e.g. Create msDS‑DelegatedManagedServiceAccount or simply Create All Child Objects. Akamai found 91 % of real‑world tenants grant such “benign” OU permissions to non‑admins.
3. Ability to run tooling (PowerShell/Rubeus) from any domain‑joined host to request Kerberos tickets.
   No control over the victim user is required; the attack never touches the target account directly.

Step‑by‑step: BadSuccessor*privilege escalation

1. Locate or create a dMSA you control

   New‑ADServiceAccount Attacker_dMSA `
       ‑DNSHostName ad.lab `
       ‑Path "OU=temp,DC=lab,DC=local"
   

Because you created the object inside an OU you can write to, you automatically own all its attributes .

2. Simulate a “completed migration” in two LDAP writes:
   • Set msDS‑ManagedAccountPrecededByLink = DN of any victim (e.g. CN=Administrator,CN=Users,DC=lab,DC=local).
   • Set msDS‑DelegatedMSAState = 2 (migration‑completed).

Tools like Set‑ADComputer, ldapmodify, or even ADSI Edit work; no domain‑admin rights are needed.

3. Request a TGT for the dMSA — Rubeus supports the /dmsa flag:

   Rubeus.exe asktgs /targetuser:attacker_dmsa$ /service:krbtgt/aka.test /dmsa /opsec /nowrap /ptt /ticket:<Machine TGT>
   

The returned PAC now contains the SID 500 (Administrator) plus Domain Admins/Enterprise Admins groups.

Gather all the users passwords

During legitimate migrations the KDC must let the new dMSA decrypt tickets issued to the old account before cut‑over. To avoid breaking live sessions it places both current‑keys and previous‑keys inside a new ASN.1 blob called KERB‑DMSA‑KEY‑PACKAGE.

Because our fake migration claims the dMSA succeeds the victim, the KDC dutifully copies the victim’s RC4‑HMAC key into the previous‑keys list – even if the dMSA never had a “previous” password. That RC4 key is unsalted, so it is effectively the victim’s NT hash, giving the attacker offline cracking or “pass‑the‑hash” capability.

Therefore, mass‑linking thousands of users lets an attacker dump hashes “at scale,” turning BadSuccessor into both a privilege‑escalation and credential‑compromise primitive.

Tools

• https://github.com/akamai/BadSuccessor
• https://github.com/logangoins/SharpSuccessor
• https://github.com/LuemmelSec/Pentest-Tools-Collection/blob/main/tools/ActiveDirectory/BadSuccessor.ps1

References

• https://www.akamai.com/blog/security-research/abusing-dmsa-for-privilege-escalation-in-active-directory