While testing our Windows Domain Controller (Server 2012 R2), I was able use the Linux utility rpcclient to enumerate user accounts and groups via a Null Session (see output below).

Checking the Windows Registry keys on the DC, I confirmed that:

  • HKLM\System\CurrentControlSet\Control\Lsa\RestrictAnonymous = 0
  • HKLM\System\CurrentControlSet\Control\Lsa\RestrictAnonymousSAM = 1
  • HKLM\System\CurrentControlSet\Control\Lsa\EveryoneIncludesAnonymous = 0

Testing the same rpcclient commands against a lab environment Server 2012 R2 DC with the exact same three Registry settings resulted in a "NT_STATUS_ACCESS_DENIED" message, as expected.

Putting aside the issue of having Null Sessions enabled in the first place... My understanding is that a value of "1" for the "RestrictAnonymousSAM" key should disable the ability to enumerate users and groups via a Null Session, so why am I still able to enumerate user information using rpcclient? Also, if the RestrictAnonymousSAM key is insufficient, what other changes are necessary to completely disable user and group enumeration via Null Sessions?

root@linuxbox:~# rpcclient -U "" {DC IP address}
Enter 's password: {empty}
rpcclient $> querydispinfo
index: 0xad08 RID: 0x122a acb: 0x00020011 Account: 000003   Name: User1 Desc:  
index: 0xab1d RID: 0x1159 acb: 0x00000010 Account: 000004   Name: User2 Desc:  
index: 0xabdc RID: 0x65c acb: 0x00000010 Account: 000009    Name: User3 Desc: 
rpcclient $> enumdomusers
user:[Administrator] rid:[0x1e5]
user:[Guest] rid:[0x1e6]
user:[krbtgt] rid:[0x1e7]
rpcclient $> enumalsgroups builtin
group:[RDS Management Servers] rid:[0x252]
group:[Hyper-V Administrators] rid:[0x253]
group:[Access Control Assistance Operators] rid:[0x254]
rpcclient $> enumalsgroups domain
group:[RAS and IAS Servers] rid:[0x229]
group:[Allowed RODC Password Replication Group] rid:[0x24c]
group:[Denied RODC Password Replication Group] rid:[0x24d]

From technet: https://technet.microsoft.com/en-us/library/jj852184(v=ws.11).aspx

This policy setting has no impact on domain controllers.

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