|Platform: win2016||Date: (C)2017-08-03 (M)2017-10-16|
"Microsoft network client: Digitally sign communications (always)"
This policy setting determines whether packet signing is required by the SMB client component. If you enable this policy setting, the Microsoft network client computer cannot communicate with a Microsoft network server unless that server agrees to sign SMB packets. In mixed environments with legacy client computers, set this option to Disabled because these computers will not be able to authenticate or gain access to domain controllers. However, you can use this policy setting in Windows 2000 or later environments.
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.
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.
Configure the settings as follows:
* Disable Microsoft Network Client: Digitally Sign Communications (Always).
* Disable Microsoft Network Server: Digitally Sign Communications (Always).
* Microsoft Network Client: Digitally Sign \Communications (If Server Agrees) to Enabled.
* Microsoft Network Server: Digitally Sign Communications (If Client Agrees) to Enabled.
In highly secure environments we recommend that you configure all of these settings to Enabled. However, that configuration may cause slower performance on client computers and prevent communications with earlier SMB applications and operating systems.
An alternative countermeasure that could protect all network traffic would be to implement digital signatures with Internet Protocol security (IPsec). There are hardware-based accelerators for IPsec encryption and signing that could be used to minimize the performance impact on the servers' CPUs. No such accelerators are available for SMB 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 Knowledgebase Article 950876 for more details: http://support.microsoft.com/kb/950876/.
(1) GPO: Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options
(2) REG: HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\LanmanWorkstation\Parameters!RequireSecuritySignature
|SCAP Repo OVAL Definition||oval:org.secpod.oval:def:40280|