Summary

• Point-to-Point Tunneling Protocol (PPTP) allows users to tunnel to an Internet Protocol (IP) network using a Point-to-Point Protocol (PPP). The protocol is described in RFC2637.

  PPTP implementation using Cisco IOSŪ software releases contains a vulnerability that will crash a router if it receives a malformed or crafted PPTP packet. To expose this vulnerability, PPTP must be enabled on the router. PPTP is disabled by default. No additional special conditions are required.

  This vulnerability is present in all Cisco IOS releases that support PPTP. PPTP is supported in the following software releases:

  • d
    
  • 12.1 train, releases: T, E, EZ, XM, XV, YA, YB, YD and YC
    
  • 12.2 train, all releases
    

  No other Cisco product is vulnerable.

  There is no workaround for this vulnerability.

  This advisory is available at https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20010712-pptp.

Affected Products

• Vulnerable Products

  This vulnerability is present in all Cisco IOS releases that support PPTP. PPTP is supported in the following releases:

  • 12.1 train, releases: T, E, EZ, XM, XV, YA, YB, YD and YC
    
  • 12.2 train, all releases
    

  To determine if a Cisco product is running an affected IOS, log in to the device and issue the command show version. Look for the "Internetwork Operating System Software" or "IOS (tm)" information, which also will have a version number. Other Cisco devices either will not have the command show version or will give different output.

  Products Confirmed Not Vulnerable

  No other Cisco products are currently known to be affected by these vulnerabilities.

Details

• By sending a crafted PPTP packet to port 1723, a control PPTP port, it is possible to crash the router. This vulnerability does not require special router configuration. Enabling PPTP is sufficient to expose the vulnerability. The router will crash after it receives a single packet.

  This vulnerability is documented as Cisco Bug ID CSCdt46181.

Workarounds

• There is no workaround for this vulnerability.

Fixed Software

• Each row of the table describes a release train and the platforms or products for which it is intended. If a given release train is vulnerable, then the earliest possible releases that contain the fix and the anticipated date of availability for each are listed in the "Rebuild," "Interim," and "Maintenance" columns. A device running a release in the given train that is earlier than the release in a specific column (less than the earliest fixed release) is known to be vulnerable. The release should be upgraded at least to the indicated release or a later version (greater than the earliest fixed release label).

  When selecting a release, keep in mind the following definitions:

  Maintenance

  Most heavily tested and highly recommended release of any label in a given row of the table.

  Rebuild

  Constructed from the previous maintenance or major release in the same train, it contains the fix for a specific defect. Although it receives less testing, it contains only the minimal changes necessary to effect the repair.

  Interim

  Built at regular intervals between maintenance releases and receives less testing. Interims should be selected only if there is no other suitable release that addresses the vulnerability. Interim images should be upgraded to the next available maintenance release as soon as possible. Interim releases are not available via manufacturing, and usually they are not available for customer download from CCO without prior arrangement with the Cisco TAC.

  In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco TAC for assistance as shown in the following section.

  More information on Cisco IOS release names and abbreviations is available at http://www.cisco.com/warp/public/620/1.html.

  Train	Description of Image or Platform	Availability of Fixed Releases*
  12.1-based Releases		Rebuild	Interim**	Maintenance
  12.1E	Core/ISP support: GSR, RSP, c7200			12.1(8a)E
  12.1E	Core/ISP support: c7100 and c7200 crypto images	12.1(7a)E1		12.1(9)E 2001-August-20
  12.1EZ	Early Deployment (ED): special image	12.1(6)EZ2
  12.1T	Early Deployment (ED): VPN, Distributed Director, various platforms	Not Scheduled
  		Upgrade recommended to 12.2(3)
  12.1XM	X Early Development (XED): limited platforms	12.1(5)XM4
  12.1XV	X Early Development (XED): limited platforms	12.1(5)XV3 2001-Jul-30
  12.1YA	Short-lived early deployment release	Not Scheduled
  		Upgrade recommended to 12.2(2)XB
  12.1YB	Early Deployment (ED): limited platforms	12.1(5)YB4
  12.1YC	Short-lived early deployment release	12.1(5)YC1
  12.1YD	Short-lived early deployment release	12.1(5)YD2
  12.2-based Releases		Rebuild	Interim**	Maintenance
  12.2	General deployment release for all platforms		12.2(1.1)	12.2(3) 2001-August
  12.2T	General deployment release for all platforms			12.2(4)T
  12.2XA	SPLOB			12.2(2)XA
  12.2XD	Short-lived early deployment release	12.2(1)XD1
  12.2XE	Short-lived early deployment release			12.2(1)XE
  12.2XH	Short-lived early deployment release			12.2(1)XH 2001-June-25
  12.2XQ	Short-lived early deployment release			12.2(1)XQ 2001-June-23
  Notes
  * All dates are estimates and subject to change. ** Interim releases are subjected to less rigorous testing than regular maintenance releases, and may have serious bugs.

Exploitation and Public Announcements

• This vulnerability was reported to Cisco by Candi Carrera from the Societe Europeenne des Satellites.

  The Cisco PSIRT received a report about potential exploitation of this vulnerability for malicious purpose against one customer.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20010712-pptp

Revision History

• Revision 1.2	2001-Sep-13	Updated status from interim to final. Updated Fixed IOS Versions table.
  Revision 1.1	2001-Jul-13	Updated train tables; summary and affected products sections.
  Revision 1.0	2001-Jul-12	Initial public release.

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