Cisco Security Advisory

ICMP Unreachable Vulnerability in Cisco 12000 Series Internet Router

Advisory ID: cisco-sa-20011114-gsr-unreachable

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20011114-gsr-unreachable

Revision 1.2

For Public Release 2001 November 14 16:00  UTC (GMT)


Summary

The performance of Cisco 12000 series routers can be degraded when they have to send a large number of ICMP unreachable packets. This situation usually can occur during heavy network scanning. This vulnerability is tracked by three different bug IDs: CSCdr46528 ( registered customers only) , CSCdt66560 ( registered customers only) , and CSCds36541 ( registered customers only) . Each bug ID is assigned to a different Engine the line card is based upon.

The rest of the Cisco routers and switches are not affected by this vulnerability. It is specific for Cisco 12000 Series.

No other Cisco product is vulnerable.

The workaround is to either prevent the router from sending unreachable Internet Control Message Protocol (ICMPs) at all or to rate limit them.

This advisory is available at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20011114-gsr-unreachable.

Affected Products

This section provides details on affected products.

Vulnerable Products

Only Cisco 12000 Series Internet Routers are affected with this vulnerability. No other routers or switches are affected. Not all line cards of the Cisco 12000 Series are affected by this vulnerability. Vulnerability is present in the underlying technology an individual line card is based upon. That technology is called "Engine". Currently, Cisco is shipping line cards based on the following Engines: 0, 1, 2, 3, and 4.

To determine what Engine your card is based on, you need to log on the Cisco 12000 router and issue the show diag command while in enable mode. The engine type will be displayed as L3 Engine: x , where x will be the corresponding number.

The following example shows the output for an Engine 2 based line card.

c12000#show diag
SLOT 1  (RP/LC 1 ): 1 Port Packet Over SONET OC-48c/STM-16 Single Mode/SR SC-SC connector
MAIN: type 41,  800-5271-01 rev A0 dev 0
HW config: 0x04    SW key: 00-00-00     
PCA:  73-3295-05 rev A0 ver 5
HW version 1.1  S/N SDK034004AY
MBUS: Embedded Agent
Test hist: 0x00    RMA#: 00-00-00    RMA hist: 0x00
DIAG: Test count: 0x00000000    Test results: 0x00000000
L3 Engine: 2 - Backbone OC48 (2.5 Gbps)

^^^^^^^^^^^^ <- Note the engine type

[further output truncated]

All line cards that are based on the Engines 0, 1 and 2 are vulnerable. Line cards based on the Engine 3 and 4 are not affected.

The following table depicts which Cisco IOS® Software Release is vulnerable to a particular issue:

DDTS

12.0S

12.0ST

CSCdr46528 ( registered customers only)

Vulnerable

Vulnerable

CSCds36541 ( registered customers only)

Vulnerable

Vulnerable

CSCdt66560 ( registered customers only)

Vulnerable

Vulnerable

Products Confirmed Not Vulnerable

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

Details

The received packet will be dropped when either there is no valid path to the destination or when the packet should be routed to the Null0 interface. The packets are either fast dropped (Engine 0 Line Cards) or hardware dropped (all other application-specific integrated circuit (ASIC) based forwarding Line Cards). Given the fast and hardware drop capabilities of the Cisco 12000, a large volume of traffic can be dropped without impacting the capabilities of the router. Whenever a packet is dropped the router must send an ICMP unreachable packet back to the source. That is mandated by the Internet Standards.

When a high volume of traffic is sent to the router that requires ICMP unreachable replies, the processing of the replies can saturate the CPU. This condition can happen when the router is "Black Hole" filtering, dropping packets sent to it as the network's default path, or from a direct Denial of Service (DOS) against the router. For further information on "Black Hole" filtering, refer to Essential IOS Features Every ISP Should Consider, section "Black Hole Routing as a Packet Filter".

The following table shows the relationship between the vulnerabilities and Engine the line card is based on.

DDTS

Engine 0

Engine 0

Engine 2

Engine 4

CSCdr46528

Vulnerable

     

CSCds36541

 

Vulnerable

   

CSCdt66560

   

Vulnerable

 

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

Exploitation of these vulnerabilities may lead to the Denial-of-Service. The router's performance will degrade and, in the worst case scenario, the router will stop forwarding packets.

Software Versions and Fixes

When considering software upgrades, also consult http://www.cisco.com/go/psirt and any subsequent advisories to determine exposure and a complete upgrade solution.

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 Technical Assistance Center ("TAC") or your contracted maintenance provider for assistance.

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 contains the fix and the anticipated date of availability for each are listed in the "Rebuild", "Interim", and "Maintenance" columns. A device running any 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, and it 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. Interim releases should be selected only if there is no other suitable release that addresses the vulnerability, and 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.

More information on Cisco IOS software 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*

Vulnerability CSCdr46528

Rebuild

Interim**

Maintenance

12.0S

Core/ISP support: GSR, RSP, c7200

12.0(16)S1

12.0(16.5)S

12.0(17)S

12.0ST

Cisco IOS software Release 12.OST is an early deployment (ED) release for the Cisco 7200, 7500/7000RSP and 12000 (GSR) series routers for Service Providers (ISPs).

12.0(15.6)ST3

12.0(16.5)ST

12.0(16)ST

Vulnerability CSCds36541

Rebuild

Interim**

Maintenance

12.0S

Core/ISP support: GSR, RSP, c7200

12.0(13.6)S2

12.0(14.1)S

12.0(14)S

12.0ST

Cisco IOS software Release 12.OST is an early deployment (ED) release for the Cisco 7200, 7500/7000RSP and 12000 (GSR) series routers for Service Providers (ISPs).

 

12.0(14.3)ST

 

Vulnerability CSCdt66560

Rebuild

Interim**

Maintenance

12.0S

Core/ISP support: GSR, RSP, c7200

12.0(16)S1

12.0(16.6)S

12.0(17)S

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 are two workarounds for this issue. The first one is to prevent the router from sending ICMP unreachables at all. That behavior is governed with the no ip unreachables command. This command should be applied on an interface, such as in this example:

router(config)#interface ethernet 0
router(config-if)#no ip unreachables

It is possible to mitigate the problem by rate limiting number of ICMP unreachables packets that are sent. Here is the example:

router(config)#ip icmp rate-limit unreachable n

Where n is the number of milliseconds between two consecutive ICMP unreachable packets. The default value is 500. That means that one ICMP unreachable packet is send every 500 ms.

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

The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability described in this advisory.

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-20011114-gsr-unreachable.

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
  • first-teams@first.org
  • bugtraq@securityfocus.com
  • vulnwatch@vulnwatch.org
  • cisco@spot.colorado.edu
  • cisco-nsp@puck.nether.net
  • full-disclosure@lists.grok.org.uk
  • comp.dcom.sys.cisco@newsgate.cisco.com

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

2006-Nov-06

Fixed URL to Black Hole filtering.

Revision 1.1

2001-Nov-15

Changed tables entries for the Affected Products and Software Versions and Fixes sections.

Revision 1.0

2001-Nov-14

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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