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Cisco Security Advisory

Cisco IOS PPTP Vulnerability

Advisory ID: cisco-sa-20010712-pptp

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20010712-pptp

Revision 1.2

For Public Release 2001 July 12 15:00  UTC (GMT)


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 IOSĀ® 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 http://tools.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.

Vulnerability Scoring Details

Cisco has provided scores for the vulnerabilities in this advisory based on the Common Vulnerability Scoring System (CVSS). The CVSS scoring in this Security Advisory is done in accordance with CVSS version 2.0.

CVSS is a standards-based scoring method that conveys vulnerability severity and helps determine urgency and priority of response.

Cisco has provided a base and temporal score. Customers can then compute environmental scores to assist in determining the impact of the vulnerability in individual networks.

Cisco has provided an FAQ to answer additional questions regarding CVSS at
http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html .

Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at
http://intellishield.cisco.com/security/alertmanager/cvss .


Impact

By repeatedly exploiting this vulnerability, it is possible to cause permanent Denial of Service (DoS). This denial is not only of the PPTP functionality but the whole router will stop functioning.

Software Versions and Fixes

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.


Workarounds

There is no workaround for this vulnerability.

Obtaining Fixed Software

Cisco has made free software available to address this vulnerability for affected customers. Prior to deploying software, customers should consult their maintenance provider or check the software for feature set compatibility and known issues specific to their environment.

Customers may only install and expect support for the feature sets they have purchased. By installing, downloading, accessing or otherwise using such software upgrades, customers agree to be bound by the terms of Cisco's software license terms found at http://www.cisco.com/public/sw-license-agreement.html, or as otherwise set forth at Cisco.com Downloads at http://www.cisco.com/public/sw-center/sw-usingswc.shtml.

Do not contact either "psirt@cisco.com" or "security-alert@cisco.com" for software upgrades.

Customers with Service Contracts

Customers with contracts should obtain upgraded software through their regular update channels. For most customers, this means that upgrades should be obtained through the Software Center on Cisco's worldwide website at http://www.cisco.com.

Customers Using Third-Party Support Organizations

Customers whose Cisco products are provided or maintained through prior or existing agreement with third-party support organizations such as Cisco Partners, authorized resellers, or service providers should contact that support organization for guidance and assistance with the appropriate course of action in regards to this advisory.

The effectiveness of any workaround or fix is dependent on specific customer situations such as product mix, network topology, traffic behavior, and organizational mission. Due to the variety of affected products and releases, customers should consult with their service provider or support organization to ensure any applied workaround or fix is the most appropriate for use in the intended network before it is deployed.

Customers Without Service Contracts

Customers who purchase direct from Cisco but who do not hold a Cisco service contract and customers who purchase through third-party vendors but are unsuccessful at obtaining fixed software through their point of sale should get their upgrades by contacting the Cisco Technical Assistance Center (TAC). TAC contacts are as follows.

  • +1 800 553 2447 (toll free from within North America)
  • +1 408 526 7209 (toll call from anywhere in the world)
  • e-mail: tac@cisco.com

Have your product serial number available and give the URL of this notice as evidence of your entitlement to a free upgrade. Free upgrades for non-contract customers must be requested through the TAC.

Refer to http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional TAC contact information, including special localized telephone numbers and instructions and e-mail addresses for use in various languages.

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.

Status of This Notice: Final

THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.

A stand-alone copy or Paraphrase of the text of this document that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors.


Distribution

This advisory will be posted on Cisco's worldwide website at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20010712-pptp.

In addition to worldwide web posting, a text version of this notice is clear-signed with the Cisco PSIRT PGP key and is posted to the following e-mail and Usenet news recipients.

  • cust-security-announce@cisco.com
  • bugtraq@securityfocus.com
  • first-teams@first.org (includes CERT/CC)
  • cisco@spot.colorado.edu
  • comp.dcom.sys.cisco
  • firewalls@lists.gnac.com
  • Various internal Cisco mailing lists

Future updates of this advisory, if any, will be placed on Cisco's worldwide website, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the above URL for any updates.


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.

Cisco Security Procedures

Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco's worldwide website at http://www.cisco.com/web/about/security/psirt/security_vulnerability_policy.html. This includes instructions for press inquiries regarding Cisco security notices. All Cisco security advisories are available at http://www.cisco.com/go/psirt.


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