Terminal Services DLL

Detection Strategy for T1505.005 – Terminal Services DLL Modification (Windows)

Audit: Auditing is the process of recording activity and systematically reviewing and analyzing the activity and system configurations. The primary purpose of auditing is to detect anomalies and identify potential threats or weaknesses in the environment. Proper auditing configurations can also help to meet compliance requirements. The process of auditing encompasses regular analysis of user behaviors and system logs in support of proactive security measures.

Auditing is applicable to all systems used within an organization, from the front door of a building to accessing a file on a fileserver. It is considered more critical for regulated industries such as, healthcare, finance and government where compliance requirements demand stringent tracking of user and system activates.This mitigation can be implemented through the following measures:

System Audit:

• Use Case: Regularly assess system configurations to ensure compliance with organizational security policies.
• Implementation: Use tools to scan for deviations from established benchmarks.

Permission Audits:

• Use Case: Review file and folder permissions to minimize the risk of unauthorized access or privilege escalation.
• Implementation: Run access reviews to identify users or groups with excessive permissions.

Software Audits:

• Use Case: Identify outdated, unsupported, or insecure software that could serve as an attack vector.
• Implementation: Use inventory and vulnerability scanning tools to detect outdated versions and recommend secure alternatives.

Configuration Audits:

• Use Case: Evaluate system and network configurations to ensure secure settings (e.g., disabled SMBv1, enabled MFA).
• Implementation: Implement automated configuration scanning tools like SCAP (Security Content Automation Protocol) to identify non-compliant systems.

Network Audits:

• Use Case: Examine network traffic, firewall rules, and endpoint communications to identify unauthorized or insecure connections.
• Implementation: Utilize tools such as Wireshark, or Zeek to monitor and log suspicious network behavior.

Restrict Registry Permissions: Restricting registry permissions involves configuring access control settings for sensitive registry keys and hives to ensure that only authorized users or processes can make modifications. By limiting access, organizations can prevent unauthorized changes that adversaries might use for persistence, privilege escalation, or defense evasion. This mitigation can be implemented through the following measures:

Review and Adjust Permissions on Critical Keys

• Regularly review permissions on keys such as Run, RunOnce, and Services to ensure only authorized users have write access.
• Use tools like icacls or PowerShell to automate permission adjustments.

Enable Registry Auditing

• Enable auditing on sensitive keys to log access attempts.
• Use Event Viewer or SIEM solutions to analyze logs and detect suspicious activity.
• Example Audit Policy: auditpol /set /subcategory:"Registry" /success:enable /failure:enable

Protect Credential-Related Hives

• Limit access to hives like SAM,SECURITY, and SYSTEM to prevent credential dumping or other unauthorized access.
• Use LSA Protection to add an additional security layer for credential storage.

Restrict Registry Editor Usage

• Use Group Policy to restrict access to regedit.exe for non-administrative users.
• Block execution of registry editing tools on endpoints where they are unnecessary.

Deploy Baseline Configuration Tools

• Use tools like Microsoft Security Compliance Toolkit or CIS Benchmarks to apply and maintain secure registry configurations.

Tools for Implementation

Registry Permission Tools:

• Registry Editor (regedit): Built-in tool to manage registry permissions.
• PowerShell: Automate permissions and manage keys. Set-ItemProperty -Path "HKLM:\Software\Microsoft\Windows\CurrentVersion\Run" -Name "KeyName" -Value "Value"
• icacls: Command-line tool to modify ACLs.

Monitoring Tools:

• Sysmon: Monitor and log registry events.
• Event Viewer: View registry access logs.

Policy Management Tools:

• Group Policy Management Console (GPMC): Enforce registry permissions via GPOs.
• Microsoft Endpoint Manager: Deploy configuration baselines for registry permissions.