Security Vulnerabilities in Microsoft PPTP

Customers using Microsoft's Point-to-Point Tunneling Protocol (PPTP) to secure communcations over a public network (i.e. the Internet) may be affected by several security issues in the encryption and authentication functions.

Issue

The Microsoft implementation of PPTP uses MS-CHAP for user authentication and Microsoft Point-to-Point Encryption (MPPE) to protect the confidentiality of user data. Potential vulnerabilities addressed by these updates include:

• Dictionary attack against the LAN Manager authentication information
• Password theft
• PPTP server spoofing
• Reuse of MPPE session keys

Solution

Microsoft released a set of patches that fix the problems identified. These patches are available for download by Windows NT, Windows 95 and Windows 98 customers from the Microsoft FTP site.

Windows NT 4.0 RAS Users

Download the patch from:
ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/NT40/hotfixes-postSP3/pptp3-fix/

Windows NT 4.0 RRAS Users

Download the patch from:
ftp://ftp.microsoft.com/bussys/winnt/winnt-public/fixes/usa/NT40/hotfixes-postSP3/rras30-fix/

Windows 95 Users

Download the patch from:
ftp://ftp.microsoft.com/softlib/mslfiles/msdun13.exe

Windows 98 Users

Download the patch from:
ftp://ftp.microsoft.com/softlib/mslfiles/dun40.exe

Further Details

Source: Microsoft Corporation

Updated: August 18, 1998

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