Summary
Affected Products
Details
Impact
Software Versions and Fixes
Workarounds
Obtaining Fixed Software
Exploitation and Public Announcements
Status of This Notice: FINAL
Distribution
Revision History
Cisco Security Procedures
A defect in multiple Cisco IOS software versions will cause a Cisco router to reload unexpectedly when the router is tested for security vulnerabilities by security scanning software programs. The defect can be exploited repeatedly to produce a consistent denial of service (DoS) attack.
Customers using the affected Cisco IOS software releases are urged to upgrade as soon as possible to later versions that are not vulnerable to this defect. Vulnerable products and releases are listed in detail below.
The security scanner is testing for the presence of two specific vulnerabilities that affect certain UNIX-based systems. The vulnerabilities are unrelated to Cisco IOS software and Cisco IOS software is not directly at risk from them. However, a side-effect of the tests exposes the defect described in this security advisory, and the router will reload unexpectedly as soon as it receives any subsequent traffic.
This defect is documented as Cisco Bug ID CSCdm70743.
This advisory is posted at http://www.cisco.com/warp/public/707/cisco-sa-20000420-ios-telnet.shtml.
This section provides details on affected products.
The following Major Releases of Cisco IOS software are vulnerable to this defect:
This vulnerability affects the following Cisco hardware products if they are running affected software:
The SC3640 System Controller is a Cisco 3640 router customized to provide local management of multiple access servers. The Cisco SC3640 binary image contains the defect and thus is vulnerable if it is possible for the attacker to telnet to the device. However, the original Cisco 3640 router does not contain the defect and is not vulnerable to the denial of service attack described in this notice.
Cisco customers running Cisco IOS software versions 11.3, 11.3T, 11.2 or lower, and 12.0(8) or 12.1 or higher are not affected. Details regarding specific releases of Cisco IOS software and suggested upgrade paths are provided below in the section "Software Versions and Fixes".
No other Cisco products are currently known to be affected by these vulnerabilities.
Software packages are available from various commercial and free sites that perform automated remote tests for computer security vulnerabilities by scanning computers on a network for known security flaws. Two security vulnerabilities associated with several UNIX-based platforms are the subject of two specific tests that have the same effect on vulnerable Cisco routers. The scanning program is asserting the Telnet ENVIRON option, #36, before the router indicates that it is willing to accept it, and this causes the router to reload unexpectedly.
The described defect can be used to mount a consistent and repeatable denial of service (DoS) attack on any vulnerable Cisco product, which may result in violations of the availability aspects of a customer's security policy. This defect by itself does not cause the disclosure of confidential information nor allow unauthorized access.
For the affected Cisco IOS software Major Release version shown in the first column of the table below, customers should upgrade to the known invulnerable releases listed to the right in the same row. In general, customers should upgrade to the release in the column furthest to the right within the same row. For example, any customer running 12.0 "mainline" (Major Release) should upgrade at least to 12.0(7.1), but preferably to 12.0(8).
Any release not specifically listed in the left-most column below is unaffected by the vulnerability.
The projected release date is shown with the software release version number for those releases that are not yet complete or available on CCO.*
An "interim release" is scheduled and contains numerous fixes and occasional enhancements that carry forward into all later versions.** A "maintenance release" is a regularly scheduled event that incorporates significant enhancements and cumulative fixes; it may be the entry point for support of noteworthy new technology in Cisco IOS software.
|
Major Release |
Description |
Projected Fixed Regular or Interim** Releases |
Projected Fixed Regular Maintenance Releases |
|---|---|---|---|
|
Unaffected Earlier Releases |
|||
|
11.2 and earlier, all variants |
Multiple releases |
Unaffected |
Unaffected |
|
11.3-based Releases |
|||
|
11.3AA |
AS5800 support and other dial platforms |
- |
11.3(11a)AA |
|
12.0-based Releases |
|||
|
12.0 |
12.0 mainline |
12.0(7.1) |
12.0(8) |
|
12.0S |
ISP support: 7200, RSP, GSR12000 |
12.0(6.6)S |
12.0(7)S |
|
12.0(7.1)S |
12.0(8)S |
||
|
12.0SC |
Cable ISP support: ubr7200 |
12.0(6.6)SC1 |
12.0(8)SC*** or 12.0(9)SC |
|
12.0(7.1)SC |
|||
|
12.0T |
12.0 new technology early deployment release |
12.0(6.5)T3 |
12.0(7)T |
|
12.0(6.5)T4 |
|||
|
12.0W |
12.0 for Catalyst 8500 and LS1010 |
12.0(6.5)W5(16.0.9) |
12.0(6.5)W5(17), 2000/04/18* |
|
12.0XE |
Short-life release for selected enterprise features, 7200 & 7500 |
Unavailable |
12.0(7)XE1 |
|
12.0XJ |
Short-life release for Dial/Voice, 5200, 5300, 5800, 2600, & 3600 |
Unavailable |
12.0(4)XJ4 |
|
12.1-based Releases |
|||
|
12.1 and later, all variants |
Multiple releases |
Unaffected |
Unaffected |
* All dates are tentative and subject to change
** Interim releases are subjected to less internal testing and verification than are regular releases, may have serious bugs, and should be installed with great care.
*** 12.0(8)SC is not vulnerable to this defect, but due to other issues it is no longer available on CCO as of the date of this notice. Upgrade instead to 12.0(9)SC.
The vulnerability described in this notice can only be exploited if the Telnet service is configured on the affected system and reachable from the attacker's computer. The following recommendations provide an interactive login capability without using the Telnet service, thus mitigating the threat in lieu of a software upgrade while preserving remote access to the router for administrative purposes:
The wide variety of customer configurations make it impossible to judge the effectiveness and relative merits of these workarounds in lieu of a software upgrade. Customers are cautioned to evaluate these recommendations carefully with regard to their specific network configurations.
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 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.
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.
As of the date of this notice, Cisco knows of no publicity, discussion, nor reports of malicious exploitation of this specific vulnerability applied directly against a Cisco product.
The denial of service (DoS) aspect of this vulnerability was reported to Cisco by several different customers who found it while conducting security scans of their networks. The defect that causes this vulnerability, documented in CSCdm70743, was discovered internally by a Cisco development engineer.
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 notice is posted at http://www.cisco.com/warp/public/707/cisco-sa-20000420-ios-telnet.shtml.
In addition to posting on the World-Wide Web, a text version of this notice is clear-signed with the Cisco PSIRT PGP key and is posted to the following e-mail lists and Usenet newsgroups:
Future updates of this notice, if any, will be placed on Cisco's World-Wide Web server, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the URL given above for any updates.
|
1.0 |
2000-April-20 |
Initial public release. |
The web page athttp://www.cisco.com/en/US/products/products_security_vulnerability_policy.html describes how to report security vulnerabilities in Cisco products, obtain assistance with security incidents, and register to receive product security information from Cisco. This includes instructions for press inquiries regarding Cisco Security Advisories and notices. This advisory is Cisco's complete public statement regarding this vulnerability.
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| Updated: Apr 20, 2000 | Document ID: 10939 |