Microsoft's PrintNightmare update is causing a lot of problems with network printers mapped on a print server

Question

Dears,
the latest Windows updates is causing a lot of problems with network printers mapped on a print server.

Reference:
KB5005652—Manage new Point and Print default driver installation behavior (CVE-2021-34481)
Managing deployment of Printer RPC binding changes for CVE-2021-1678 (KB4599464)

The two recent patches (KB5004945, KB5004760, or KB5003690) causes these two main problems:

1. unable for users without administrative rights to install new print drivers.
   The end user receive this error
   

2) unable to use the print server with the new registry key RpcAuthnLevelPrivacyEnabled
The system logs reports this error: 0x0000011b

The two workarounds that you have to apply to survive and allow corporate users to be able to use the print server are:

1. Even if you have a GPO with "Point and Print Restrictions=disabled", you have to apply this registry key to allow non administrative users to install the latest print drivers from the print server

HKEY_LOCAL_MACHINE\Software\Policies\Microsoft\Windows NT\Printers\PointAndPrint
RestrictDriverInstallationToAdministrators = 0

2) Apply this registry key to disable the new default settings related to the print spooler vulnerabilities

HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Print
RpcAuthnLevelPrivacyEnabled = 0

The above workarounds are only a temporary solution to survive and allow users to print.
What is unclear to me is what should be the right way to manage these settings in a corporate environment without any end user interaction.
So, if I want to be protected and apply the recent security fixes without asking the end users to do something, what should I do?

Microsoft states that you need to set "RpcAuthnLevelPrivacyEnabled" to "1" on both Client and Print Server in order to be protected, but if you do this, you can't print.
So, what should we do in a Corporate environment to be secure and print without any end user interaction about "driver installation" etc.?

Thanks in advance

Answer 1

I would like to know the answer to this as well.

The only way that I have been able to print from a client computer is to set RpcAuthnLevelPrivacyEnabled = 0 on the server. This allows me to install the printer from the server.

RpcAuthnLevelPrivacyEnabled setting on the client's computer has no effect.

I have also attempted to enable Point and Print Restrictions to limit the client computers to specific servers, but it has no effect on the machines. I can still download printers from any server. I'm not sure what I am missing to make that GPO configuration work.

Does anyone have any ideas or suggestions?

Answer 2

Hi Norbert ,It looks like you are not using the Windows Standard TCP/IP port, is there a specific reason for this? I am guessing the port monitor is some HP code. To be fair, Windows Standard TCP/IP port was ffrom HP, they licensed it to Microsoft in 1997 to be included in Windows 2000. Switch the port first. I don't expect this UI.

Answer 3

is there a fix for a corporate environment ?
we have had the same issue - but it seems we need to change the key back n forth just to get the printer installed.
there has to be a fix without adding users security to the printer itself.

thank you

Answer 4

The only thing that I have found that works is to set RpcAuthnLevelPrivacyEnabled = 0 on the print server found here HKLM\SYSTEM\CurrentControlSet\Control\Print.

From my testing, it appears that this option tells the connecting computer to use Administrative Credentials. I do not see how this would be a fix to the PrintNightmare vulnerability because the connecting computer could still add a printer from another print server that is compromised.

We still run into the issue that unsigned drivers require administrator privileges to install or update the driver. Luckily, we do not have many printers that are using unsigned drivers.

Answer 5

@thenewmessiah

The new Windows default for Point an Print connections to shared printers is admin rights.

You can work through this with the registry setting on the client system.

The "RpcAuthnLevelPrivacyEnabled" set to 1 prevents the client systems, and the print server, from connecting to Linux machines pretending to be Windows print servers. Do you have Linux in your environment where you may have concerns?

To work through no administrative requirements for connections to Windows shared printers, then you can use a print driver on the server which is never downloaded to the client system. These drivers are known as Type 4 print drivers. You can find these on Windows update and from printer vendors. Type 4 print drivers have existed for nine years. More than 10 if you used Windows 8 in preview versions.

Since there is no software copied making the printer connection, then the attack service is gone.

There are group policies to specifically provide access to only print servers you control and if you manage all the Windows clients I also suggest closing down the remote spooler RPC endpoint on the client systems. Disable the Computer policy which Allow clients to connect to spooler . If the client is actually sharing a printer, the RPC endpoint is open but how many Windows clients are sharing a printer in your organization?

If you obtain your Type 4 drivers from Windows Update or if you are running 2012R2 you can use the drivers provided with the operating system. The client can get the driver from WU if a Type 4 driver is up there.

Admin rights for printer connection when software is downloaded from the server. It's the new world of Windows and it will not be changing.

Thanks