Network security: LAN Manager authentication level

NTLM is a challenge/response protocol where in the authenticating server or domain controller issues a challenge which the client authenticates using the password hash as a key. NTLM has been repeatedly patched over the years to address security vulnerabilities. The oldest Windows systems can only send back the LM response originally developed in the 80s for LanManager. With NT Microsoft developed a stronger hash and response mechanism called NTLM but continued supporting LM. Vulnerabilities were found in NTLM prompting NTLMv2. For more information on NTLM see “Network security: Do not store LAN Manager hash value on next password change”.

These patches affect connectivity to/from older versions of Windows and this setting allows you to tweak NTLM on this computer to be strict and less compatible with older systems or more compatible but less secure. Note that the values for this setting impact how the computer handles NTLM authentication both as a client and as the authenticating server. Microsoft documentation describes how this setting affects domain controllers but the correction terminology would be authenticating server since this setting impacts both domain controllers (when authenticating a domain account) and workstations and member servers (when authenticating a local SAM account). To control how Active Directory will handle NTLM configure this setting on your domain controllers using the Default Domain Controllers Policy GPO. To control how a workstation or member server will handle NTLM when authenticating local SAM accounts or – more often – when functioning as an NTLM client, configure this setting in an applicable group policy object that is applied to the desired computers.

NTLMv2 Session Security

Another issue impacted by this policy is NTLMv2 Session Security. Session security is a feature of the NTLN SSPI that allows applications to encrypt and/or sign communication between client and server after initial authentication is complete. Session keys are not used during the actual authentication sequence, but when an application requests security by calling the EncryptMessage or SignMessage APIs. NTLMv2 Session Security protects against certain man-in-the-middle attacks by improving how the session key is generated.

Also read : microsoft lan manager

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