Securing domain controllers

Domain controllers are essential to keeping Active Directory running. Contributor Derek Melber recommends these Group Policy settings to lock down your DC.

A majority of companies have taken the plunge by installing Windows Active Directory in the enterprise and, for most, it is controlling a large portion of the network. Microsoft has increased the default security within Active Directory, especially if you have a Windows Server 2003 Active Directory installation, but you still need to consider additional security settings after it is installed.

For more information
  • Tip: An introduction to ADFS
  • Book excerpt: Administrator shortcut guide to Active Directory security
  • There are very sophisticated attackers that exist on your current network. You might not know who they are, but they are lurking at all times. The domain controllers need to be protected from such attackers at all costs. Examples of network protection that you should consider implementing include:

    • Use of Group Policy to secure domain controllers
    • Denial of anonymous user access
    • Use of IP Security for replicating Active Directory data
    • Limiting the LAN manager authentication protocols that are supported

    In order to secure network access to a domain controller, Group Policy settings need to be configured. The following is a list of Group Policy settings (under the Computer Configuration\Windows Settings\Security Settings\Local Policies node) that can help protect access to a domain controller and its contents:

    Node Policy Suggested setting
    User Rights Assignment Allow logon locally Only administrator type groups
    Allow logon through Terminal Services Only administrator type groups
    Back up files and folders Only administrator type groups
    Security Options Network access: Allow anonymous SID/Name translation Disabled
    Network access: Do not allow anonymous enumeration of SAM accounts and shares Enabled
    Network access: Let Everyone permissions apply to anonymous users Disabled
    Network access: Shares that can be accessed anonymously COMCFG, DFS$
    Network security: LAN Manager authentication level Send NTLMv2 response only/ refuse LM and NTLM (must be tested to ensure compatibility with legacy clients and applications)
    Network security: Do not store LAN Manager hash value on next password change Enabled

    Challenge: Try making an anonymous connection to one of your domain controllers and then, using a tool like DumpSec, GetAccnt, or Winfingerprint, enumerate shared folders or user names. To create an anonymous connection just type the following at a command prompt: Net use \\ ipc$ /u:"" ""

    If it works, you've got a security problem in your network.

    Note: As with any Registry or security modification, be sure to test the settings before putting them into your production environment. There are many configurations, applications, and unique environments that don't support all good security practices and settings.

    About the author: Derek Melber, MCSE, MVP, and CISM, is the director of compliance solutions for DesktopStandard Corp. He has written the only books on auditing Windows security available at The Institute of Internal Auditors' bookstore and also wrote the Group Policy Guide for Microsoft Press -- the only book Microsoft has written on Group Policy. You can contact Melber at derekm@desktopstandard.com.


    This was first published in October 2005

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