Fixing vulnerabilities on Active Directory (AD) servers requires a systematic approach to identify, prioritize, and remediate security weaknesses while maintaining the integrity and availability of the AD environment.
1. Identify Vulnerabilities
• Perform Regular Vulnerability Scans: Use tools like Nessus, Qualys, or Microsoft Defender for Identity to scan AD servers for known vulnerabilities, misconfigurations, and weak settings.
• Audit AD Configuration: Leverage tools like BloodHound, PingCastle, or Purple Knight to analyze AD for privilege escalation risks, weak permissions, or overly permissive accounts.
• Monitor Security Logs: Check Event Viewer logs (e.g., Event IDs 4624, 4672, 4741) for suspicious activity, such as unauthorized access or privilege changes.
• Review Microsoft Security Advisories: Stay updated on Common Vulnerabilities and Exposures (CVEs) specific to AD, such as PrintNightmare (CVE-2021-34527) or PetitPotam (CVE-2021-36942).
2. Apply Security Patches
• Patch Operating Systems: Ensure AD servers (typically Windows Server) are updated with the latest security patches from Microsoft. Use Windows Server Update Services (WSUS) or Microsoft Endpoint Configuration Manager for centralized patch management.
• Patch AD-Specific Vulnerabilities: Apply fixes for AD-specific CVEs. For example:
• Kerberos Vulnerabilities: Address issues like CVE-2020-17049 (Kerberos KDC vulnerability) by applying relevant patches and configuring secure Kerberos settings.
• Netlogon (Zerologon, CVE-2020-1472): Ensure patches are applied and enforce secure RPC settings as per Microsoft’s guidance.
• Automate Patching: Schedule regular updates but test patches in a non-production environment first to avoid disruptions.
3. Harden AD Configuration
• Implement Least Privilege:
• Restrict Domain Admin and Enterprise Admin accounts to essential personnel.
• Use Privileged Access Management (PAM) solutions like Microsoft Privileged Access Workstations (PAWs) for administrative tasks.
• Remove unnecessary accounts from privileged groups (e.g., Domain Admins, Schema Admins).
• Secure Group Policies:
• Review and lock down Group Policy Objects (GPOs) to prevent unauthorized changes.
• Disable outdated protocols like NTLMv1 and SMBv1, which are prone to exploitation.
• Enable Secure LDAP (LDAPS): Ensure all LDAP traffic uses LDAPS (port 636) with valid certificates to prevent eavesdropping.
• Restrict Anonymous Access: Disable anonymous binds to AD and enforce authentication for all queries.
• Secure Kerberos:
• Enable AES encryption for Kerberos (disable RC4).
• Implement Account Lockout Policies to prevent brute-force attacks on service accounts.
4. Mitigate Common AD Attack Vectors
• Prevent Credential Theft:
• Deploy Microsoft’s Local Administrator Password Solution (LAPS) to randomize local admin passwords.
• Restrict NTLM usage and monitor for Pass-the-Hash or Pass-the-Ticket attacks.
• Enable Credential Guard on Windows Server to protect against credential dumping.
• Secure Kerberoasting:
• Use strong passwords (20+ characters) for service accounts.
• Monitor for SPN (Service Principal Name) enumeration attempts.
• Block DCSync Attacks:
• Restrict replication rights to only necessary accounts.
• Monitor for unusual replication requests (Event ID 4662).
• Prevent Golden/Silver Ticket Attacks:
• Rotate the KRBTGT account password regularly (at least every 180 days).
• Use Microsoft Defender for Identity to detect forged Kerberos tickets.
5. Enhance Authentication Security
• Enable Multi-Factor Authentication (MFA):
• Use Azure AD or third-party solutions to enforce MFA for admin accounts and privileged access.
• Integrate with Conditional Access policies if using Azure AD.
• Use Strong Password Policies:
• Enforce complex passwords (minimum 14 characters, no common phrases).
• Regularly audit for weak or reused passwords using tools like DSInternals.
• Limit Service Account Permissions: Ensure service accounts have minimal privileges and are not used for interactive logins.
6. Monitor and Respond to Threats
• Deploy SIEM Solutions: Use tools like Splunk, Microsoft Sentinel, or Azure Monitor to collect and analyze AD logs for suspicious activity.
• Enable Advanced Auditing:
• Configure audit policies for account logon, account management, and directory service access.
• Monitor for signs of reconnaissance, such as excessive LDAP queries.
• Set Up Alerts: Create alerts for critical events, such as changes to privileged groups or failed logon attempts by sensitive accounts.
• Incident Response Plan: Develop and test a response plan for AD compromises, including isolating affected servers and resetting credentials.
7. Secure Physical and Network Access
• Isolate Domain Controllers:
• Place AD servers in a dedicated VLAN with strict firewall rules.
• Limit RDP access to domain controllers and use jump servers for administrative access.
• Use Secure Backups: Regularly back up AD using tools like Windows Server Backup and store backups offline to prevent ransomware attacks.
• Network Segmentation: Prevent lateral movement by segmenting networks and restricting communication between AD servers and non-essential systems.
8. Address Specific Vulnerabilities
• PrintNightmare (CVE-2021-34527):
• Disable the Print Spooler service on domain controllers if not needed.
• Apply Microsoft patches and restrict printer driver installation permissions.
• PetitPotam (CVE-2021-36942):
• Disable NTLM authentication where possible.
• Enable Extended Protection for Authentication (EPA) on AD servers.
• SAMR/SAMBA Vulnerabilities: Restrict SAMR (Security Account Manager Remote) protocol access to only authorized systems.
9. Educate and Train Staff
• Train administrators on secure AD management practices and phishing awareness.
• Conduct regular security awareness training for all users to prevent social engineering attacks that could compromise AD credentials.
10. Regularly Test and Validate
• Penetration Testing: Conduct regular red team exercises to simulate AD attacks (e.g., Kerberoasting, DCSync).
• Backup and Recovery Testing: Verify that AD backups can be restored successfully in a disaster recovery scenario.
• Update Documentation: Maintain detailed documentation of AD configurations, changes, and security measures.
Additional Notes
• Prioritize Based on Risk: Use vulnerability scan results and tools like PingCastle to prioritize high-risk issues (e.g., accounts with SID history, weak ACLs).
• Leverage Microsoft Defender for Identity: This tool provides real-time detection of AD-specific attacks like reconnaissance, lateral movement, and privilege escalation.
• Stay Updated: Follow Microsoft’s Security Update Guide and subscribe to X posts or RSS feeds from security researchers for real-time updates on AD vulnerabilities.