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Category:   OS (Microsoft)  >   Windows PPTP Service Vendors:   Microsoft
(Microsoft Issues Fix) Microsoft PPTP Service Buffer Overflow May Let Remote Users Execute Arbitrary Code
SecurityTracker Alert ID:  1005501
SecurityTracker URL:  http://securitytracker.com/id/1005501
CVE Reference:   CVE-2002-1214   (Links to External Site)
Date:  Oct 31 2002
Impact:   Denial of service via network, Execution of arbitrary code via network, Root access via network
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): Windows 2000, XP
Description:   A buffer overflow vulnerability was reported in Microsoft's point-to-point protocol (PPTP) service. A remote user can cause the system to crash and may be able to execute arbitrary code.

phion Information Technologies issued a security advisory warning of a pre-authentication buffer overflow affecting both the PPTP client and server implementation.

A remote user can send a specially crafted PPTP packet to overwrite kernel memory and crash the system. It is also possible to overwrite the EDI and EDX registers and, according to the report, potentially execute arbitrary shell code.

The vendor has reportedly been notified.

Impact:   A remote user can cause the system to crash. A remote user may be able to execute arbitrary code on the system.
Solution:   Microsoft has released patches for Windows 2000 and XP:

For Microsoft Windows 2000:

http://www.microsoft.com/downloads/Release.asp?ReleaseID=43606

For Microsoft Windows XP:

32-bit: http://www.microsoft.com/downloads/Release.asp?ReleaseID=43635
64-bit: http://www.microsoft.com/downloads/Release.asp?ReleaseID=43631

Microsoft reports that the Windows 2000 patch can be installed on Windows 2000 SP2 or SP3 and the patch for Windows XP can be installed on Windows XP Gold or SP1.

The vendor plans to include the fix for this issue in Windows 2000 SP4 and Windows XP SP2.

Microsoft plans to release Knowledge Base article Q329834 regarding this issue, to be available shortly on the Microsoft Online Support web site at:

http://support.microsoft.com/?scid=fh;en-us;kbhowto

Vendor URL:  www.microsoft.com/technet/security/bulletin/MS02-063.asp (Links to External Site)
Cause:   Boundary error
Underlying OS:  Windows (2000), Windows (XP)

Message History:   This archive entry is a follow-up to the message listed below.
Sep 26 2002 Microsoft PPTP Service Buffer Overflow May Let Remote Users Execute Arbitrary Code



 Source Message Contents

Subject:  Microsoft Security Bulletin MS02-063: Unchecked Buffer in PPTP Implementation Could Enable Denial of Service Attacks (Q329834)


-----BEGIN PGP SIGNED MESSAGE-----

- ----------------------------------------------------------------------
Title:      Unchecked Buffer in PPTP Implementation Could Enable
            Denial of Service Attacks (Q329834)
Date:       30 October 2002
Software:   Windows 2000, Windows XP
Impact:     Denial of Service
Max Risk:   Critical 
Bulletin:   MS02-063

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS02-063.asp.
- ----------------------------------------------------------------------

Issue:
======
Windows 2000 and Windows XP natively support Point-to-Point Tunneling
Protocol (PPTP), a Virtual Private Networking technology that is
implemented as part of Remote Access Services (RAS). PPTP support is
an optional component in Windows NT 4.0, Windows 98, Windows 98SE,
and Windows ME. 

A security vulnerability results in the Windows 2000 and Windows XP
implementations because of an unchecked buffer in a section of code
that processes the control data used to establish, maintain and tear
down PPTP connections. By delivering specially malformed PPTP control
data to an affected server, an attacker could corrupt kernel memory
and cause the system to fail, disrupting any work in progress on the
system. 

The vulnerability could be exploited against any server that offers
PPTP. If a workstation had been configured to operate as a RAS server
offering PPTP services, it could likewise be attacked. Workstations
acting as PPTP clients could only be attacked during active PPTP
sessions. Normal operation on any attacked system could be restored
by restarting the system.

Mitigating Factors:
====================
 - As discussed in more detail in the FAQ, Microsoft has only 
   successfully demonstrated denial of service attacks via this 
   vulnerability. Because of how the overrun occurs, it does not 
   appear that that there is any reliable means of using it to gain
   control over a system. 
 - Servers would only be at risk from the vulnerability if they
   had been specifically configured to offer PPTP services. PPTP does
   not run by default on any Windows system. Likewise, although it 
   is possible to configure a workstation to offer PPTP services, 
   none operate in this capacity by default. 
 - Exploiting the vulnerability against a PPTP client could be 
   difficult. PPTP is typically used in scenarios in which the client
   IP address changes frequently (e.g., because the client system is
   mobile). Not only would an attacker need to learn the IP address, 
   but he or she would also need to mount an attack while the client
   had an active PPTP session underway.

Risk Rating:
============
 - Internet systems: Critical
 - Intranet systems: Low
 - Client systems: Low

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read the 
   Security Bulletin at
   http://www.microsoft.com/technet/security/bulletin/ms02-063.asp
   for information on obtaining this patch.

- ---------------------------------------------------------------------

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS 
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE 
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE
FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO
THE FOREGOING LIMITATION MAY NOT APPLY.

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