Active Directory is still one of the most critical components of enterprise security, yet it remains one of the most frequently targeted systems by attackers. According to Microsoft Incident Response, nearly every investigation they handle involves a total domain compromise. This occurs when threat actors gain complete control of Active Directory, often starting with the takeover of a standard user account before escalating to Domain Admin.
Recovering from this type of breach can take months of work and significant investment. That is why Microsoft emphasizes the need for continuous improvement in Active Directory security rather than treating it as a one-time project.
How Attackers Gain Initial Access
Weak Passwords and Credential Hygiene
Weak password policies are one of the most common entry points for attackers. Password spraying and brute-force attacks succeed far too often, especially when organizations allow privileged accounts to rely on guessable credentials. If VPN or remote access is enabled without multi-factor authentication, stolen or weak passwords give attackers a simple path into the network.
Service accounts also create risk. Many are overprivileged, not rotated frequently, and excluded from MFA. In some cases, administrators store service account credentials in plain text within scripts or configuration files, making them easy targets.
Insecure Account Configurations
Microsoft Incident Response regularly uncovers accounts with dangerous settings such as “password not required” or reversible encryption enabled. Attackers can quickly identify these accounts during reconnaissance and use them to escalate privileges.
The Path to Credential Theft
Once inside, attackers focus on privileged credential exposure. Cached administrator credentials on non-Tier 0 systems are often harvested with tools like Mimikatz or Impacket. The wider administrators log into end user devices and servers, the greater the attack surface becomes.
Attackers also rely on Kerberoasting, a technique that abuses service principal names (SPNs). By requesting Kerberos tickets and cracking them offline, attackers can gain access to high-privilege service accounts. Insecure delegation settings create another pathway, allowing attackers to impersonate users if they compromise systems that store Kerberos tickets in memory.
Escalation to Full Domain Compromise
With footholds established, attackers take advantage of deeper weaknesses:
- Misconfigured Access Control Lists (ACLs): Overly permissive ACLs allow compromised accounts to add themselves to privileged groups or rewrite security settings.
- Exchange Permissions: On-premises Exchange environments often retain extensive Active Directory privileges, even in hybrid deployments. Attackers who gain SYSTEM-level access to Exchange servers can escalate to domain control.
- Group Policy Abuse: Group Policy Objects (GPOs) are frequently misused to disable endpoint defenses, establish persistence, or distribute ransomware.
- Trust Relationships: Poorly secured domain trusts, particularly during mergers and acquisitions, open cross-domain attack paths for adversaries.
Each of these misconfigurations shortens the path from a compromised user account to full control of the domain.
Expanding Definition of Tier 0
In the past, Tier 0 referred mainly to domain controllers. Today, it also includes Active Directory Federation Services (ADFS), Azure AD Connect, and certificate services. Compromising any of these identity systems can provide attackers with the same level of control as compromising a domain controller.
Organizations must treat every Tier 0 asset with the same protection strategy. This includes requiring privileged access workstations, restricting local admin rights, and monitoring all identity infrastructure as part of a Zero Trust approach.
Building a Stronger Defense for Active Directory
From Microsoft’s perspective, most compromises are caused by recurring issues: weak passwords, excessive privileges, misconfigured ACLs, and insecure delegation. To strengthen Active Directory security, organizations should adopt a continuous improvement cycle:
- Reduce Privilege: Apply the principle of least privilege, limit the number of Domain Admin accounts, and require the use of privileged access workstations for Tier 0 systems.
- Audit Regularly: Use Microsoft Defender for Identity, BloodHound, and PingCastle to identify misconfigurations and lateral movement paths.
- Monitor Changes: Track account creations, group membership changes, and permission modifications that could introduce new attack paths.
- Detect Actively: Deploy detections for Kerberoasting, unconstrained delegation abuse, and other suspicious Active Directory activities.
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