Stopping Lateral Movement via Windows Admin Shares

Stopping lateral movement in Windows environments.

The Windows Admin Shares—particularly the hidden ADMIN$ share—are a critical component of Windows network administration, enabling remote management, software deployment, and patch installation. However, these shares are a double-edged sword: they are a favorite target for adversaries attempting Lateral Movement, a core tactic defined by the MITRE ATT&CK framework as T1021.002: Remote Services: SMB/Windows Admin Shares.

The modern security environment demands that our response to an "Access to ADMIN$ Share detected" alert moves beyond simple log checks to an integrated, behavioral-based approach utilizing next-generation Endpoint Detection and Response (EDR) and Security Orchestration, Automation, and Response (SOAR) tools.

1. The Modern Threat: Why ADMIN$ is Still Dangerous

The old playbook focused on whether an admin account was compromised; the modern threat is more subtle. Attackers often "Live off the Land" (LotL) by using native Windows tools like PowerShell, PsExec, or WMI over the SMB protocol to interact with the ADMIN$ share. This allows them to:

• Stage Payloads: Copy malicious files to the remote system's %SystemRoot% directory via the ADMIN$ share.

• Execute Remotely: Use a stolen, valid credential to execute that payload using other remote execution techniques (like Scheduled Tasks or Windows Services).

• Blend In: Because these activities use legitimate, built-in tools, they easily blend into normal network traffic, making detection harder for legacy tools.

2. Updated Investigation Protocol (The TDIR Approach)

When a Security Information and Event Management (SIEM) or EDR tool alerts on unauthorized access to the ADMIN$ share, the Security Operations Center (SOC) analyst's investigation (part of the Detection, Investigation, and Response—TDIR—lifecycle) should be swift and highly correlated.

A. Initial Triage & Contextualization

The initial purpose of this playbook remains to highlight the unusual behavior that may reveal malicious activity.

• Identify the Attacker's Tooling: Look beyond the SMB connection itself. Search EDR and command logs for the execution of common lateral movement tools immediately before or after the ADMIN$ connection: PsExec, Impacket tools (e.g., smbexec.py), or a suspicious PowerShell command with remote functionality.

• Source/Destination Context: Verify the source and destination IP addresses and hostnames. Does a workstation typically access the ADMIN$ share of another workstation or a server? Is the source a known Privileged Access Workstation (PAW)? (If not, any administrative connection is immediately suspicious.)

• User/Account Analysis: Check the account's privilege level and group membership. Critically, investigate if the user account was recently compromised, for example, through a Kerberoasting or Credential Dumping attack detected earlier in the logs.

B. Deep-Dive Investigation

• Behavioral Correlation: If an ADMIN$ share access is detected, immediately pivot to the destination host's EDR logs. Look for a subsequent suspicious process execution, service creation, or new scheduled task originating from the network share. This is the action phase of the attack.

• Credential Check: Review authentication logs (e.g., Kerberos or NTLM) for the compromised account. Were there recent failed login attempts that could indicate brute-forcing leading to a compromise?

• Historical Analysis: Develop a historical baseline of the host and user. Has this machine or user performed administrative remote actions before? If not, the incident should be immediately escalated.

3. Modern Defense & Countermeasures (Shifting Left)

The most effective response is proactive prevention, making lateral movement pathways "dead end". The old countermeasure of "patching" must be augmented by strategic identity and network controls.

A. Identity and Privilege Control (The Priority)

1. Enforce Least Privilege: Implement a solution to remove local admin rights from standard users on all workstations. This is the single most effective way to stop the majority of lateral movement techniques. Use Application-level Elevation or just-in-time (JIT) administrative access instead.

2. Tiered Access Model: Adopt Microsoft's Enterprise Access Model (superseding the old Administrative Tier Model). Isolate your most critical assets (Tier 0) like Domain Controllers and AD FS servers, ensuring they are only managed by Tier 0 accounts from dedicated Privileged Access Workstations (PAWs).

3. Phishing-Resistant MFA: Apply Multi-Factor Authentication (MFA) not only for external access but also for privileged internal accounts and services, making stolen credentials less useful for lateral movement.

4. Implement LAPS: Deploy a Local Administrator Password Solution (LAPS) to ensure the local administrator password is unique and complex on every machine.

B. Network and Host Hardening

1. Microsegmentation: Use an identity-aware microsegmentation strategy to restrict workstation-to-workstation communications, forcing traffic through monitored servers and limiting the ability of a compromised workstation to reach others.

2. Disable SMBv1 & Harden SMB: Apply hardening guidelines to services like SMB. While disabling the ADMIN$ share is a strong security measure, it's often impractical, so focus on controlling who can access it.

3. Regular Patching: Maintain a routine process for patching known exploited vulnerabilities, as attackers frequently exploit these for privilege escalation before lateral movement.

C. SOC Automation

The final countermeasure is using SOAR to automate containment. Playbooks should be highly automated to reduce Mean Time to Respond (MTTR). Upon confirmation of malicious activity:

• Automatically isolate the source host.

• Force-change the compromised user's password.

• Create a ticket with all correlated evidence and a severity score (Dynamic Risk Scoring), reducing alert fatigue and focusing analysts' time.