What is Network security: Restrict NTLM: NTLM authentication in this domain policy setting?

Written by Titus Manohar, IT security team, ManageEngine  •  Updated on April 2026

Network security: Restrict NTLM: NTLM authentication in this domain setting is used to block NTLM authentication on a specific domain. This policy applies only to the domain controller on which it is set. NTLM is an older Windows authentication software that has been known to be vulnerable to man-in-the-middle (MITM) attacks, brute force attacks, SMB relay and so on. Therefore a network administrator can choose to put in place a domain-wide restriction on NTLM authentication using this policy.

Following are the possible values for this setting:

• Disable: There is no restriction on NTLM authentication requests in this domain.
• Deny for domain accounts to domain servers: This option blocks the NTLM authentication requests from domain accounts to domain servers unless the server is on the list of server exceptions created by enabling Network security: Restrict NTLM: Add server exceptions setting in that domain.
• Deny for domain accounts: This option blocks NTLM authentication requests from all domain accounts unless the server is on the list of server exceptions created by enabling Network security: Restrict NTLM: Add server exceptions setting in that domain.
• Deny for domain servers: Enabling this blocks all NTLM authentication requests to domain servers unless the server is on the list of server exceptions created by enabling Network security: Restrict NTLM: Add server exceptions setting in that domain.
• Deny all: This option blocks all authentication requests to servers from all accounts unless the server is on the list of server exceptions created by enabling Network security: Restrict NTLM: Add server exceptions setting in that domain.
• Not defined: This policy is not defined and the domain controller will allow all NTLM authentication requests.

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