PPTP Performance & Security Upgrade for WinNT 4.0 Release Notes

MORE INFORMATION

Point to Point Tunneling Protocol (PPTP) performance and security upgrade for Microsoft Windows NT Server 4.0 and Microsoft Windows NT Workstation release notes

Please use this document to address questions that may arise during the installation of this PPTP Performance & Security Upgrade for Microsoft Windows NT 4.0 Server and Workstation.

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Contents

• Information on Installation
• Security Features in this Upgrade
• Fixes and Features included from the 2.0 Hotfix

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Installation information

Microsoft has made improvements to the native Virtual Private Networking (VPN) capabilities of Windows client and server that significantly improve the performance and security PPTP-based VPN connections via the Internet for Windows NT Server and Windows NT Workstation version 4.0.

This upgrade should be applied to both Windows NT Servers and Windows NT Workstations version 4.0. Service Pack 3 for Windows NT 4.0 must also be installed before applying this update.

Note Windows NT Servers running Routing and Remote Access Service (RRAS) must first apply this Windows NT PPTP performance upgrade followed by the RRAS Hotfix 3.0 to benefit from the upgrade (it is important not to reboot your machine in-between installations of the NT PPTP upgrade & the Routing and Remote Access Service upgrade).

For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

This upgrade is packaged in an auto-install format. It is recommended that you first copy the upgrade to a temporary directory, and then double-click the executable name or type the executable name pptpfixi.exe for x86 or pptpfixa.exe for alpha at a command prompt to install.

The files can also be extracted from the Upgrade pack without installing them. To do this, copy the Upgrade to a temporary directory, and type pptpfixi /x or pptpfixa /x at a command prompt. After extracting the files, the Upgrade can be installed by typing hotfix at a command prompt.

To uninstall this upgrade, extract the files to a directory using the "/x" command as mentioned above and then type HOTFIX -Y from the same directory you copied the files to.

Output of HOTFIX -?:

HOTFIX [-y] [-f] [-n] [-z] [-q] [-m] [-l]

      -y Perform uninstall (only with -m or -q)
      -f Force apps closed at shutdown
      -n Do not create uninstall directory
      -z Do not reboot when update completes
      -q Quiet Mode -- no user interface
      -m Unattended mode
      -l List installed hotfixes
				

Security features in this upgrade

This upgrade provides several RAS/PPTP security enhancements for Microsoft Windows NT 4.0. This upgrade also includes the performance improvements and other fixes that were included in previously released PPTP hotfixes for Windows NT Service Pack 3.

• A new version of MSCHAP (MSCHAP V2) has been implemented for VPN connections. This new protocol provides mutual authentication, stronger initial data encryption keys, and different encryption keys for the transmit and receive paths. To minimize the risk of password compromise during MSCHAP exchanges, MSCHAP V2 drops support for the MSCHAP password change V1, and will not transmit the LMHash encoding of the password.
  
  For VPN connection requests, a Windows NT server will offer MSCHAP V2 before offering the legacy MSCHAP. Updated Windows clients (all platforms) will accept MSCHAP V2 when it is offered. This behavior affects only VPN connections; dial-up connections are not affected.
• A new registry key, SecureVPN, has been defined to force use of MSCHAP V2. When this variable is absent it has a default value of zero. When set to one on a Windows NT server, this registry key causes the server to drop any VPN connections that do not authenticate using MSCHAP V2. This will prevent legacy VPN clients from presenting their credentials in an MSCHAP (or CHAP or PAP) exchange, and is a likely configuration for networks that require a more secure authentication method for VPN connections.
  HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\RasMan\P
  DWORD: SecureVPN Value: 0x00000001 == force MSCHAP V2 for VPN connections Value: 0x00000000 == do not force secure MSCHAP V2 (defaul
  
  When set to one on a Windows NT 4.0 client, the SecureVPN registry key forces the client to use MSCHAP V2 for all VPN (PPTP) connections. Dial-up connections are not affected by this registry setting.
  
  Please note: Most users will not need to use the Secure VPN flag. This flag should be used with care because it will affect the behavior of all VPN connections from a client. In general, the required use of MSCHAP V2 can be enforced more easily on the server.
• This release also provides a registry variable, UseLmPassword, which can be set to prevent clients from sending the LM response to a legacy MSCHAP challenge or in an MSCHAP change password exchange. When this variable is absent it has a default value of one, allowing use of the LM response (in order to maintain compatibility with legacy systems).
  HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\RasMan\PPP\Ch
  DWORD: UseLmPassword Value: 0x00000001 == send LMHash of the password (default) Value: 0x00000000 == do not send LMHash of the passwo
  
  Setting this variable to zero on a server will cause the server to drop any connection request which uses the LM response in an MSCHAP exchange. Setting this variable to zero on a client will prevent the client from using LM responses in MSCHAP exchanges. This variable affects BOTH dial-up and VPN connections.
  
  Please note: Most users will not need to use this registry variable. The new secure mode MSCHAP V2 will not send the LMHash response, so this registry value is most useful when connecting to older access servers which use the original MSCHAP.

Fixes and features included in the 2.0 Hotfix

PPTP performance issues that are addressed in this update

• A new historyless mode for encryption & compression over PPTP connections has been enabled. This new mode will dramatically improve performance using PPTP in high latency networks, or networks that commonly experience significant packet loss like the Internet. This upgrade is fully compatible with legacy PPTP systems. However, in order to negotiate historyless mode, both the PPTP client and server must support the upgrade. If either client or server refuses the new mode, normal MPPE compression and encryption will be negotiated to insure communication capabilities are not lost. To experience the full benefit of the PPTP performance update, this update must be installed on both Windows NT clients and servers. A corresponding release Microsoft Dial-Up Networking 1.3 is available for Windows 95 clients, while the new release of Windows 98 already includes the appropriate client code.
  
  Please note: RAS Servers that terminate compulsory PPTP connections from an FEP (Front End Processor) must disable historyless compression/encryption in order for legacy Windows 95 clients to receive data properly. An FEP is a dial-up server which can create a PPTP tunnel on behalf of its dial-up clients. This feature is available from several Access Server vendors, including Compaq (Microcom), Ascend, and 3com.
  
  The value to set in the registry to enable/disable historyless encryption/compression is:
  HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NdisWan\Paramete
  DWORD: Historyless Value: 0x00000001 == Enabled (default) Value: 0x00000000 == Disabl
• The default PPTP receive window size was increased to 16.
• The window between the NDISWAN driver and the PPTP driver was increased.
• The PPTP frame size has been set to default to 1400 bytes to avoid packet fragmentation.
  
  Please note: The frame size issue was also addressed in an earlier hotfix, and is documented at:

  http://support.microsoft.com/support/kb/articles/q162/2/30.asp

Remote Access Service and PPTP issues

• PPTP server responsiveness has been improved for the time period right after termination of multiple PPTP connections.
• A PPTP server issue of an improperly configured packet header "start session" has been corrected. This issue is documented at:

  http://support.microsoft.com/support/kb/articles/q179/1/07.asp

• Improved integrity of session encryption in MPPE by increasing the randomness of successive packet key management following an encryption or compression reset.
• Corrected a RAS/PPTP user interface design issue that could mislead an administrator regarding the actual configuration of the server. This issue is documented at:

  http://support.microsoft.com/support/kb/articles/q177/6/70.asp

• Updated MSCHAP to disable sending the LMHash when client set to "require" 128-bit encryption.

Other Windows NT issues that are addressed in this update

• This release includes an enhancement to TCP/IP which will improve the performance of TCP-based applications over high latency networks, such as the Internet.

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