Advisory ID: cisco-sa-20020812-vpnclient-vulnerability
For Public Release 2002 August 12 15:00 UTC (GMT)
Multiple vulnerabilities exist in the Cisco Virtual Private Network (VPN) Client software. Exploitation of these vulnerabilities prevents the Cisco VPN Client software program from functioning correctly.
These vulnerabilities are documented as Cisco bug ID CSCdy26045. There are no workarounds available to mitigate the effects of these vulnerabilities.
This advisory will be posted at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20020812-vpnclient-vulnerability.
This section provides details on affected products.
The VPN Client software program runs on the following platforms:
- Microsoft Windows-based PC.
- Red Hat Version 6.2 Linux (Intel), or compatible distribution, using kernel Version 2.2.12 or later. It does not support kernel Version 2.5.
- Solaris UltraSPARC running a 32-bit kernel OS Version 2.6 or later.
- Mac OS X Version 10.1.0 or later.
All VPN Client software programs, earlier than version 3.6 and earlier than version 3.5.4, on all platforms are affected by this vulnerability. This includes the previous Cisco Secure VPN Client and the the Cisco VPN 3000 Client software programs.
Cisco VPN 5000 Client software programs are not affected by this vulnerability.
No other Cisco products are currently known to be affected by these vulnerabilities.
The VPN Client software program on a remote workstation, communicating with a Cisco VPN device on an enterprise network or with a service provider, creates a secure connection over the Internet. Through this connection you can access a private network as if you were an on-site user.
The VPN Client software program has been found to have the following vulnerabilities:
- An Internet Key Exchange (IKE) packet with a Security Parameter Index (SPI) payload containing more than 16 bytes causes a buffer overflow in the VPN client software.
- An IKE packet with more than 57 valid payloads causes a buffer overflow in the VPN Client software.
- When the VPN Client software receives a specially crafted packet with a zero length payload, it causes the VPN Client software to use 100% of CPU resources on the workstation.
These vulnerabilities are documented as Cisco bug ID CSCdy26045, which requires a CCO account to view. CSCdy26045 can be viewed after 2002 August 13 at 1500 UTC.
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
Cisco has also provided a CVSS calculator to help compute the environmental impact for individual networks at
When the vulnerabilities are exploited they prevent the Cisco VPN Client software program from functioning correctly. The Cisco VPN Client software program's availability may be impacted. There is no impact to the confidentiality and integrity of the data.
This vulnerability has been fixed in Cisco VPN Client version 3.6 or later, which is now available for download. The fix for this vulnerability will also be integrated in VPN Client version 3.5.4 or later, and will be available for download by September 30, 2002.
The procedure to upgrade to the fixed software version on the various platforms is detailed in the documentation available at http://www.cisco.com/univercd/cc/td/doc/product/vpn/client/.
There are no workarounds for these vulnerabilities. The Cisco PSIRT recommends that affected users upgrade to a fixed software version of code.
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 "email@example.com" or "firstname.lastname@example.org" for software upgrades.
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 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 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: email@example.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.
The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerabilities described in this advisory.
These vulnerabilities were reported to PSIRT by CERT/CC and were discovered by Anton Rager of Avaya Security Consulting Services.
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.
This advisory will be posted on Cisco's worldwide website athttp://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20020812-vpnclient-vulnerability.
In addition to worldwide website posting, a text version of this advisory is clear-signed with the Cisco PSIRT PGP key having the fingerprint FEB1 1B89 A64B 60BB 4770 D1CE 93D2 FF06 F236 759C and is posted to the following e-mail and Usenet news recipients:
- firstname.lastname@example.org (includes CERT/CC)
- 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.
Initial public release.