Detections
Analytics

2.3.8.1 Ensure 'Microsoft network client: Digitally sign communications (always)' is set to 'Enabled'

Warning! Audit Deprecated

This audit has been deprecated and will be removed in a future update.

View Next Audit Version

Information

This policy setting determines whether packet signing is required by the SMB client component.

Note: When Windows Vista-based computers have this policy setting enabled and they connect to file or print shares on remote servers, it is important that the setting is synchronized with its companion setting,
Microsoft network server: Digitally sign communications (always)
, on those servers.

For more information about these settings, see the 'Microsoft network client and server: Digitally sign communications (four related settings)' section in Chapter 5 of the Threats and Countermeasures guide.

The recommended state for this setting is: 'Enabled'.

Rationale:

Session hijacking uses tools that allow attackers who have access to the same network as the client or server to interrupt, end, or steal a session in progress.

Attackers can potentially intercept and modify unsigned SMB packets and then modify the traffic and forward it so that the server might perform undesirable actions.

Alternatively, the attacker could pose as the server or client after legitimate authentication and gain unauthorized access to data.

SMB is the resource sharing protocol that is supported by many Windows operating systems.

It is the basis of NetBIOS and many other protocols.

SMB signatures authenticate both users and the servers that host the data.

If either side fails the authentication process, data transmission will not take place.

Solution

To establish the recommended configuration via GP, set the following UI path to 'Enabled':

Computer Configuration\Policies\Windows Settings\Security Settings\Local Policies\Security Options\Microsoft network client: Digitally sign communications (always)

Impact:

The Microsoft network client will not communicate with a Microsoft network server unless that server agrees to perform SMB packet signing.

The Windows 2000 Server, Windows 2000 Professional, Windows Server 2003, Windows XP Professional and Windows Vista implementations of the SMB file and print sharing protocol support mutual authentication, which prevents session hijacking attacks and supports message authentication to prevent man-in-the-middle attacks.

SMB signing provides this authentication by placing a digital signature into each SMB, which is then verified by both the client and the server.

Implementation of SMB signing may negatively affect performance, because each packet needs to be signed and verified.

If these settings are enabled on a server that is performing multiple roles, such as a small business server that is serving as a Domain Controller, file server, print server, and application server performance may be substantially slowed.

Additionally, if you configure computers to ignore all unsigned SMB communications, older applications and operating systems will not be able to connect.

However, if you completely disable all SMB signing, computers will be vulnerable to session hijacking attacks.

When SMB signing policies are enabled on Domain Controllers running Windows Server 2003 and member computers running Windows Vista SP1 or Windows Server 2008 group policy processing will fail.

A hotfix is available from Microsoft that resolves this issue; see Microsoft Knowledge Base article 950876 for more details: [Group Policy settings are not applied on member computers that are running Windows Server 2008 or Windows Vista SP1 when certain SMB signing policies are enabled](https://support.microsoft.com/en-us/kb/950876).

See Also

https://workbench.cisecurity.org/files/1933

Item Details

Category: IDENTIFICATION AND AUTHENTICATION

References: 800-53|IA-3, CCE|CCE-35222-9, CSCv6|13

Plugin: Windows

Control ID: a742d9c24b56998caffef574fa7bbc19db0d49bc6427b7961934027931fdf26a