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

2002-10-31T00:00:00
ID SECURITYVULNS:DOC:3699
Type securityvulns
Reporter Securityvulns
Modified 2002-10-31T00:00:00

Description

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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.

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