Monday, July 18, 2016

Network shares might become inaccessible after installation of KB3161949

In this case, access to internal network shares for external users was granted over Cisco ASA as a published solution. After installation of KB3161949 on Window Server 2012 R2, that was hosting those network shares, the network shares become inaccessible to these external users. The error message that external users were experiencing by the Cisco ASA portal was "Error contacting host":

Even though the description of this KB is "MS16-077 Description of the security update for WPAD: June 14, 2016", there is a change by this KB affecting the network shares access.
The first change listed in the KB article is hardening the NETBIOS communication outside of the local subnet, affecting the SMB over NETBIOS to stop working outside of the local subnet (in my case Cisco ASA for publishing network share access was relying on).
Resolving the issue for these external users, and enabling access to internal shares same way as before installation of this KB, was either by uninstalling the KB or enabling the following key in registry:

SUBKEY: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NetBT\Parameters
Value Name: AllowNBToInternet
Type: Dword
Value: 1

After creation of AllowNBToInternet and setting the value to 1, and rebooting the server, external users were able to connect to network shares again, hosted on Windows Server 2012 R2 and published by Cisco ASA.

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