Network security: Minimum session security for NTLM SSP based (including secure RPC) clients

Updated: November 15, 2012

Applies To: Windows 7, Windows Server 2003, Windows Server 2008, Windows Server 2008 R2, Windows Vista, Windows XP

This security policy reference topic for the IT professional describes the best practices, location, values, policy management and security considerations for this policy setting.

Reference

This policy setting allows a client computer to require the negotiation of 128-bit encryption or NTLMv2 session security. These values are dependent on the Network security: LAN Manager Authentication Level policy setting value.

Possible values

• Require NTLMv2 session security

  The connection fails if strong encryption (128-bit) is not negotiated.

• Require 128-bit encryption

  The connection fails if the NTLMv2 protocol is not negotiated.

Best practices

Practices in setting this policy are dependent on your security requirements.

Location

GPO_name\Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options

Default values

The following table lists the actual and effective default values for this policy. Default values are also listed on the policy’s property page.

Operating system version differences

In Windows Server 2008 and earlier versions of the Windows operating system, no requirements were set. But in computers running Windows Server 2008 R2 Require 128-bit encryption is the default.

In Windows Server 2008 R2 and Windows 7, only 128-bit encryption or NTLMv2 session security options are available.

Policy management

This section describes features and tools that are available to help you manage this policy.

Restart requirement

None. Changes to this policy become effective without a computer restart when they are saved locally or distributed through Group Policy.

Policy conflicts

The settings for this security policy are dependent on the Network security: LAN Manager Authentication Level policy setting value. For information about this policy, see Network security: LAN Manager authentication level.

Security considerations

This section describes how an attacker might exploit a feature or its configuration, how to implement the countermeasure, and the possible negative consequences of countermeasure implementation.

Vulnerability

Network traffic that uses the NTLM Security Support Provider (NTLM SSP) could be exposed such that an attacker who has gained access to the network can create man-in-the-middle attacks.

Countermeasure

Enable all options that are available for the Network security: Minimum session security for NTLM SSP based (including secure RPC) clients policy setting.

Potential impact

Client computers that enforce these settings cannot communicate with older servers that do not support them.