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Cisco Security Advisory

Multiple Vulnerabilities in Access Control List Implementation for Cisco 12000 Series Internet Router

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

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

Revision 1.1

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


Summary

Six vulnerabilities involving Access Control List (ACL) has been discovered in multiple releases of Cisco IOS® Software Release for Cisco 12000 Series Internet Routers. Not all vulnerabilities are present in all IOS releases and only line cards based on the Engine 2 are affected by them.

No other Cisco product is vulnerable.

The workarounds are described in the Workarounds section.

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

Affected Products

This section provides details on affected products.

Vulnerable Products

Only Cisco 12000 Series Internet Routers with line cards based on Engine 2 are affected with these vulnerabilities. Not all line cards of a Cisco 12000 Series are affected by all vulnerabilities. Vulnerabilities are 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 "sh 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#sh 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] 

These vulnerabilities are affecting line cards based on Engine 2.

Products Confirmed Not Vulnerable

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

Details

Six vulnerabilities were found in IOS releases that are supporting Cisco 12000 platforms. Only line cards based on Engine 2 are affected.

  • CSCdm44976
    ACL will not block non initial fragments of a packet. This Cisco bug ID is adding a support for "fragment" keyword in the ACL. The White Paper Access Control Lists and IP Fragments describes how keyword fragment modifies behavior of ACL.
  • CSCdu57417
    The keyword "fragment" in the compiled ACL (Turbo ACL) is ignored if a packet is destined to the router itself.
  • CSCdu03323
    The implicit "deny ip any any" rule at the end of an ACL is ignored if an ACL of exactly 448 entries is applied on an interface as an outgoing ACL. An ACL with any other number of rules, greater or less than 448, is unaffected by this vulnerability.
  • CSCdu35175
    A support for "fragment" keyword in an outgoing ACL is added. Previously, only incoming ACL supported this keyword and outgoing ACL was ignoring it.
  • CSCdt96370
    An outbound Access Control List (ACL) may not block all intended traffic on a router when an input ACL is configured on some, but not all, interfaces of a multi port Engine 2 line card. The prerequisite is that, the traffic in question, was not filtered by an inbound ACL on the ingress port. An ACL applied at the ingress point will work as expected and block desired traffic.
  • CSCdt69741
    Packet fragments are not filtered by the ACL despite using "fragment" keyword. The White Paper Access Control Lists and IP Fragments describes how keyword fragment modifies behavior of ACL.

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

  • CSCdm44976
    The router will not block all traffic. By sending an offending traffic in packet fragments it is possible to circumvent the protection offered by ACL and cause Denial-of-Service for the protected IP address.
  • CSCdu57417
    It is possible to cause the Denial-of-Service on the router itself if sufficient amount of traffic is sent to the router. This offending traffic should be send as packet fragments.
  • CSCdu03323
    If an outgoing ACL contains exactly 448 entries and if explicit rule "deny ip any any" is not present as the last statement, the ACL will fail to drop packets. Our tests shows that only 50% of packets are dropped. This may allow some undesired traffic to pass into the protected network thus violating security policy.
  • CSCdu35175
    Fragmented packets may be allowed into the protected network if the keyword "fragment" was applied to an outgoing ACL.
  • CSCdt96370
    This vulnerability can cause unwanted traffic to be allowed in and out of the protected network. The security based on an ACL will be breached completely.
  • CSCdt69741
    This vulnerability can be exploited to attack systems that are supposed to be protected by the ACL on the router.

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 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.

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 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 CSCdm4476

Rebuild

Interim**

Maintenance

12.0S

Core/ISP support: GSR, RSP, c7200

 

12.0(10.1)S

12.0(11)S

Vulnerability CSCdu57417

Rebuild

Interim**

Maintenance

12.0S

Core/ISP support: GSR, RSP, c7200

 

12.0(19.3)S

12.0(19)S

12.0ST

Early deployment (ED) release for the Cisco 7200, 7500/7000RSP and 12000 series routers for Service Providers (ISPs).

12.0(18.6)ST1

12.0(19.3)ST

12.0(19)ST

Vulnerability CSCdu03323

Rebuild

Interim**

Maintenance

12.0S

Core/ISP support: GSR, RSP, c7200

12.0(16)S2

12.0(17.5)S

12.0(17)S

12.0ST

Early deployment (ED) release for the Cisco 7200, 7500/7000RSP and 12000 series routers for Service Providers (ISPs).

12.0(16.6)ST1

12.0(17.5)ST

12.0(17)ST

Vulnerability CSCdu35175

Rebuild

Interim**

Maintenance

12.0S

Core/ISP support: GSR, RSP, c7200

 

12.0(19.6)S

 

12.0ST

Early deployment (ED) release for the Cisco 7200, 7500/7000RSP and 12000 series routers for Service Providers (ISPs).

 

12.0(19.6)ST

 

Vulnerability CSCdt96370

Rebuild

Interim**

Maintenance

12.0S

Core/ISP support: GSR, RSP, c7200

12.0(16)S1

12.0(17.1)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(17.1)ST

12.0(16)ST

Vulnerability CSCdt69741

Rebuild

Interim**

Maintenance

12.0S

Core/ISP support: GSR, RSP, c7200

12.0(16.6)S2

12.0(17.3)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(17.3)ST

12.0(18)ST

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

CSCddm44976

There is no direct workaround for this vulnerability. If feasible, packet fragments may be filtered before they reach the GSR.

CSCdu57417

There is no direct workaround for this vulnerability. If feasible, packet fragments may be filtered before they reach the GSR.

CSCdu03323

The workaround is to either shorten the ACL to be less than 448 lines in length or to explicitly add rule "deny ip any any" as the last statement.

CSCdu35175

The workaround is to transform an ACL to an incoming ACL instead of the outgoing one.

CSCdt96370

Apply an ACL on all ports on the ingress line card. If a particular port is supposed to not block any traffic, then apply the ACL of the form access-list xy permit ip any any.

CSCdt69741

There is no direct workaround for this vulnerability. It is possible to block the fragments on an intermediate router, if such exists, that should be placed between the affected Cisco 12000 and the final target. The intermediate router must not be another Cisco 12000 affected by the same 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

The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerabilities 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 notice will be posted on Cisco's Worldwide Web site at http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20011114-gsr-acl. 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 notice, if any, will be placed on Cisco's Worldwide 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.


Revision History

Revision 1.1

2001-November-15

Update table with fixed IOS releases

Revision 1.0

2001-November-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 Web site 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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