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1.1.1.2.1.27 Set 'Network security: LAN Manager authentication level' to 'Send NTLMv2 response only. Refuse LM & NTLM'

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

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Information

LAN Manager (LM) is a family of early Microsoft client/server software that allows users to link personal computers together on a single network. Network capabilities include transparent file and print sharing, user security features, and network administration tools. In Active Directory domains, the Kerberos protocol is the default authentication protocol. However, if the Kerberos protocol is not negotiated for some reason, Active Directory will use LM, NTLM, or NTLMv2. LAN Manager authentication includes the LM, NTLM, and NTLM version 2 (NTLMv2) variants, and is the protocol that is used to authenticate all Windows clients when they perform the following operations: . Join a domain . Authenticate between Active Directory forests . Authenticate to down-level domains . Authenticate to computers that do not run Windows 2000, Windows Server 2003, or Windows XP) . Authenticate to computers that are not in the domain The possible values for the Network security: LAN Manager authentication level setting are: . Send LM & NTLM responses . Send LM & NTLM use NTLMv2 session security if negotiated . Send NTLM responses only . Send NTLMv2 responses only . Send NTLMv2 responses only\refuse LM . Send NTLMv2 responses only\refuse LM & NTLM . Not Defined The Network security: LAN Manager authentication level setting determines which challenge/response authentication protocol is used for network logons. This choice affects the authentication protocol level that clients use, the session security level that the computers negotiate, and the authentication level that servers accept as follows: . Send LM & NTLM responses. Clients use LM and NTLM authentication and never use NTLMv2 session security. Domain controllers accept LM, NTLM, and NTLMv2 authentication. . Send LM & NTLM use NTLMv2 session security if negotiated. Clients use LM and NTLM authentication and use NTLMv2 session security if the server supports it. Domain controllers accept LM, NTLM, and NTLMv2 authentication. . Send NTLM response only. Clients use NTLM authentication only and use NTLMv2 session security if the server supports it. Domain controllers accept LM, NTLM, and NTLMv2 authentication. . Send NTLMv2 response only. Clients use NTLMv2 authentication only and use NTLMv2 session security if the server supports it. Domain controllers accept LM, NTLM, and NTLMv2 authentication. . Send NTLMv2 response only\refuse LM. Clients use NTLMv2 authentication only and use NTLMv2 session security if the server supports it. Domain controllers refuse LM (accept only NTLM and NTLMv2 authentication). . Send NTLMv2 response only\refuse LM & NTLM. Clients use NTLMv2 authentication only and use NTLMv2 session security if the server supports it. Domain controllers refuse LM and NTLM (accept only NTLMv2 authentication). These settings correspond to the levels discussed in other Microsoft documents as follows: . Level 0 Send LM and NTLM response; never use NTLMv2 session security. Clients use LM and NTLM authentication, and never use NTLMv2 session security. Domain controllers accept LM, NTLM, and NTLMv2 authentication. . Level 1 Use NTLMv2 session security if negotiated. Clients use LM and NTLM authentication, and use NTLMv2 session security if the server supports it. Domain controllers accept LM, NTLM, and NTLMv2 authentication. . Level 2 Send NTLM response only. Clients use only NTLM authentication, and use NTLMv2 session security if the server supports it. Domain controllers accept LM, NTLM, and NTLMv2 authentication. . Level 3 Send NTLMv2 response only. Clients use NTLMv2 authentication, and use NTLMv2 session security if the server supports it. Domain controllers accept LM, NTLM, and NTLMv2 authentication. . Level 4 Domain controllers refuse LM responses. Clients use NTLM authentication, and use NTLMv2 session security if the server supports it. Domain controllers refuse LM authentication, that is, they accept NTLM and NTLMv2. . Level 5 Domain controllers refuse LM and NTLM responses (accept only NTLMv2). Clients use NTLMv2 authentication, use and NTLMv2 session security if the server supports it. Domain controllers refuse NTLM and LM authentication (they accept only NTLMv2). In Windows Vista, this setting is undefined. However, in Windows 2000, Windows Server 2003, and Windows XP clients are configured by default to send LM and NTLM authentication responses (Windows 95-based and Windows 98-based clients only send LM). The default setting on servers allows all clients to authenticate with servers and use their resources. However, this means that LM responses the weakest form of authentication response are sent over the network, and it is potentially possible for attackers to sniff that traffic to more easily reproduce the user's password. The Windows 95, Windows 98, and Windows NT operating systems cannot use the Kerberos version 5 protocol for authentication. For this reason, in a Windows Server 2003 domain, these computers authenticate by default with both the LM and NTLM protocols for network authentication. You can enforce a more secure authentication protocol for Windows 95, Windows 98, and Windows NT by using NTLMv2. For the logon process, NTLMv2 uses a secure channel to protect the authentication process. Even if you use NTLMv2 for earlier clients and servers, Windows-based clients and servers that are members of the domain will use the Kerberos authentication protocol to authenticate with Windows Server 2003 domain controllers.

Solution

To implement the recommended configuration state, set the following Group Policy setting to 5.

Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options\Network security- LAN Manager authentication level

Impact- Clients that do not support NTLMv2 authentication will not be able to authenticate in the domain and access domain resources by using LM and NTLM. Note- For information about a hotfix to ensure that this setting works in networks that include Windows NT 4.0-based computers along with Windows 2000, Windows XP, and Windows Server 2003-based computers, see article 305379, Authentication Problems in Windows 2000 with NTLM 2 Levels Above 2 in a Windows NT 4.0 Domain, in the Microsoft Knowledge Base (http-//go.microsoft.com/fwlink/?LinkId=100907).

See Also

https://workbench.cisecurity.org/files/42

Item Details

Category: IDENTIFICATION AND AUTHENTICATION

References: 800-53|IA-5(6), CCE|CCE-3703-6

Plugin: Windows

Control ID: a42b386e1659e3091acdd8c5d886c543277cc6c5be2f2a19d7f67e137c254122