How to Identify and Exploit Entra ID Synchronization Servers

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Introduction

Entra ID (formerly Azure AD) synchronization servers play a critical role in hybrid identity environments, syncing on-premises Active Directory with cloud-based Entra ID. However, misconfigurations or weak security controls can turn these servers into high-value targets for attackers. This article explores how to identify the synchronization server and exploit it using NetExec, a powerful offensive security tool.

Learning Objectives

  • Identify the Entra ID synchronization server using AD attributes.
  • Exploit the server to extract MSOL account credentials.
  • Leverage DCSync privileges for domain compromise.

1. Locating the Entra ID Synchronization Server

Verified Command (PowerShell/AD Query)

Get-ADUser -Identity "ADSyncMSA" -Properties msDS-HostServiceAccountBL, Description

Step-by-Step Guide

  1. The `ADSyncMSA` service account is created during Entra ID Connect setup.
  2. Query its `msDS-HostServiceAccountBL` attribute, which references the sync server.
  3. The `Description` field of the MSOL account may also contain the server name.

2. Compromising the Sync Server with NetExec

Verified NetExec Command

nxc smb <TARGET_IP> -u <USER> -p <PASSWORD> --module entra-id-sync

Step-by-Step Guide

  1. Use NetExec to authenticate to the target server (SMB protocol).
  2. The `entra-id-sync` module extracts MSOL credentials stored in the sync service.
  3. These credentials often have DCSync privileges, allowing full domain replication.

3. Exploiting DCSync for Domain Takeover

Verified Mimikatz Command

lsadump::dcsync /domain:<DOMAIN> /user:krbtgt

Step-by-Step Guide

  1. With MSOL credentials, use Mimikatz to perform a DCSync attack.

2. Extract the `krbtgt` account’s NTLM hash.

3. Forge Golden Tickets for persistent domain access.

4. Mitigation: Hardening Entra ID Sync Servers

Verified GPO Hardening Command

Set-GPPermission -Name "EntraSyncHardening" -Replace -PermissionType Deny -TargetName "Authenticated Users"

Step-by-Step Guide

1. Restrict administrative access to the sync server.

  1. Disable unnecessary services and enforce LAPS for local admin passwords.

3. Monitor `msDS-HostServiceAccountBL` changes for anomalies.

5. Detecting Suspicious Sync Server Activity

Verified Sigma Detection Rule

title: Entra ID Sync Server Exploitation 
description: Detects MSOL credential extraction attempts 
logsource: 
product: windows 
service: security 
detection: 
selection: 
EventID: 4662 
ObjectType: "MSOL_" 
condition: selection

Step-by-Step Guide

  1. Deploy SIEM rules to monitor `EventID 4662` (object access).
  2. Alert on any access to MSOL account attributes.

What Undercode Say

  • Key Takeaway 1: Entra ID sync servers are prime targets due to their DCSync privileges.
  • Key Takeaway 2: NetExec simplifies exploitation, but defenders can mitigate risks with strict access controls.

Analysis:

The integration of on-prem AD and Entra ID creates attack paths that many organizations overlook. While tools like NetExec expose these vulnerabilities, proactive hardening—such as limiting service account permissions and auditing sync servers—can prevent catastrophic breaches. As hybrid environments grow, expect more automated attacks targeting synchronization services.

Prediction

Future attacks will likely abuse Entra ID sync for lateral movement in cloud-centric breaches. Microsoft may enforce stricter defaults, but admins must act now to secure these critical nodes.

IT/Security Reporter URL:

Reported By: Alexander Neff – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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