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

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.
    

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.

Fixed Software

• 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.

Exploitation and Public Announcements

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

URL

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

Revision History

• Revision 1.1	2001-November-15	Update table with fixed IOS releases
  Revision 1.0	2001-November-14	Initial public release

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