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      How to Disable Null Session in Windows

      In a Windows environment, null sessions can allow users to have anonymous access to hidden administrative shares on a system.

      Once connected to the shares through a null session, attackers can potentially enumerate information about your system and environment, such as users and groups, operating systems, password policies, privileges, etc. With this information, an attacker can learn about any potential vulnerabilities or ways to best attack your systems.

      Disabling null sessions is a key way to help you strengthen your organization's security and reduce your attack surface.

      Edit GPO- Go to Computer configuration\Policies\Windows settings\Security Settings\Local Policies\SecurityOptions

      Enable:

      • Network access: Restrict Anonymous access to Named Pipes and Shares
      • Network access: Do not allow anonymous enumeration of SAM accounts
      • Network access: Do not allow anonymous enumeration of SAM accounts and shares
      • Network access: Shares that can be accessed anonymously
      Disable:
      • Network access: Let Everyone permissions apply to anonymous users
      • Network access: Allow anonymous SID/Name translation
      • Restrict Null Sessions in the Registry
      If you open regedit and browse to:
      • HKLM\System\CurrentControlSet\Control\Lsa\RestrictAnonymous
        • 1 - Null sessions can not be used to enumerate shares
      • HKLM\System\CurrentControlSet\Control\Lsa\RestrictAnonymousSAM
        • 1 - Default setting. Null sessions can not enumerate user names
      • HKLM\System\CurrentControlSet\Control\Lsa\EveryoneIncludesAnonymous
        • 0 - Default setting. Null sessions have no special rights

      null-sessions

      Figure 1: Modifying the RestrictAnonymous key in the registry

      Disable smbv1 via PowerShell

      There are a wide variety of exploits for smbv1. Follow recommended settings and steps via the Microsoft Support article for your Operating System. Sources:

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