Advisory ID: cisco-sa-20010328-vpn3k-telnet
For Public Release 2001 March 28 16:00 UTC (GMT)
Sending a flood of data to the SSL or regular telnet port can cause the Cisco VPN 3000 series concentrators to reboot. After rebooting, the equipment would function normally until the flood of data is sent again.
To remove the vulnerability, Cisco is offering free software upgrades to revision 2.5.2(F) for all affected platforms. The defect is described in companion DDTS's CSCds90807 and CSCds64223.
This notice will be posted at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20010328-vpn3k-telnet
This section provides details on affected products.
Cisco VPN 3000 series concentrators running software releases up to but not including version 2.5.2(F) are affected by this vulnerability. This series includes models 3005, 3015, 3030, 3060, and 3080. Any model running version 2.5.2(F) or later is unaffected by this vulnerability.
To determine if a Cisco VPN 3000 series concentrator is running affected software, check version via the web interface or the console login.
This vulnerability does not affect the VPN 5000 series concentrators. No other Cisco product is affected by this vulnerability.
No other Cisco products are currently known to be affected by these vulnerabilities.
The vulnerability occurs because the SSL or regular telnet session does not disconnect after repeated failed attempts and the system keeps trying to interpret the data coming in on the SSL or regular telnet port. Therefore, data coming in at an uncontrolled rate can flood the telnet queues causing a shortage of memory on the system resulting in a reboot. This has been fixed by ensuring that a SSL or regular telnet session is terminated after three repeated failed attempts. The vulnerability is documented in two companion DDTS's CSCds90807 and CSCds64223.
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
Sending a flood of data to the SSL or regular telnet port can cause the VPN 3000 series concentrators to reboot. While reloading, the device cannot handle any traffic. Repeatedly causing the affected device to reload will result in a denial of service, thus affecting the availability of the device.
SSL and regular telnet service on the external interface is disabled by default.
The vulnerability has been fixed in revision 2.5.2(F) code. The fix will be carried forward into all future releases.
The vulnerability can be avoided by disabling all Telnet access to the equipment until you upgrade.
There are two ways to disallow telnet on any given interface - you can use a filter whose rules don't allow telnet, or by creating a rule that specifically denies telnet access and applying that to your existing filter(s).
Further details can be found at the this URL http://www.cisco.com/univercd/cc/td/doc/product/vpn/vpn3000/vpn3kco/vcoug/usr_3_0/polmgt.htm
After disabling SSL and regular telnet the equipment can be managed via the console port or via browser access.
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. This was reported to Cisco by a customer who discovered this vulnerability as a side effect of using a SSL telnet tool.
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 at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20010328-vpn3k-telnet.
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.
- 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.
Change in revision of fixed software
Initial public release.