Security researchers at Microsoft have released a PowerShell script that aims at stopping attackers from pulling off reconnaissance in a compromised network.
The tool, Net Case, was released late last week and modifies Net Session Enumeration (NetSessionEnum) default permissions so that if an attacker enters a network from a specific end point, they won’t be able to jump to a new target in that same network to gather intel. If unprotected, those who have breached a network can gather personal information, including name of specific PCs and IP addresses, session active and idle information, and names of those who have opened a specific session through the NetSessionEnum. Net Case looks to block the access points to the information that could easily be accessible through the use of tools like the widely available NetSess tool.
“Once attackers had ‘zoomed in’ on target users, they need to find out the computers they had logon to, in order to propagate to them and compromise their credentials, explained Microsoft Researcher Itai Grady, in a blog post announcing the tool’s availability. “Applying the SMB Session enumeration via the NetSessionEnum method against the DC (or other file servers), allows the attackers to get that information. Recently, some frameworks (e.g. BloodHound) have automated that mapping process.”
How Net Cease protects against this is by adding permissions to batch login sessions and blocking Authenticated Users group from executing permissions. This will block access to the private network information from an unauthorized user. Further, Net Cease will automatically alert network and system admins when an attempted information inquiry has been launched through Microsoft Advanced Threat Analytics.
Grady explained that due to the nature of the NetSessionEnum, hardening it could not be accomplished through a traditional update. ” Since the only current method to modify the default permissions for NetSessionEnum is by manually editing hex registry entry, we wrote the ‘NetCease’ tool, a short PowerShell (PS) script which alters these default permissions.”This hardening process should block attackers from easily getting valuable recon information.”
Those looking to implement the tool will need to run the PowerShell script as an administrator on servers and systems. A server or system restart may need to occur before it goes into effect.
Net Cease has been tested to work with all currently supported versions of Windows OS and Windows Server, including Windows 10 and Windows Server 2016. The tool, along with additional information, can be downloaded here.