M-018: Cisco - Multiple Vulnerabilities in ACL Implementations

[***** Start Cisco Security Advisory: Revision 1.1 *****]




Cisco Security Advisory: Multiple Vulnerabilities in Access Control List 

Implementation for Cisco 12000 Series Internet Router



Revision 1.1



For Public Release 2001 November 14 08:00 (UTC -0800)



Last Update 2001 November 15 12:00 (UTC -0800)





Summary



Six vulnerabilities involving Access Control List (ACL) has been discovered in 

multiple releases of Cisco IOSŪ 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://www.cisco.com/warp/public/707/GSR-ACL-pub.shtml 





Affected 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. 





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. 





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. 

 





Obtaining Fixed Software



Cisco is offering free software upgrades to eliminate this vulnerability for all 

affected customers. 



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 Web site 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 

assistance with the upgrade, which should be free of charge. 



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 



Please 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. 



Please do not contact either "psirt@cisco.com" or "security-alert@cisco.com" for 

software upgrades. 





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. 





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 is a final notice. Although Cisco cannot guarantee the accuracy of all 

statements in this notice, all of the facts have been checked to the best of our 

ability. Cisco does not anticipate issuing updated versions of this notice unless 

there is some material change in the facts. Should there be a significant change in 

the facts, Cisco may update this notice. 



A standalone copy or paraphrase of the text of this security advisory 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://www.cisco.com/warp/public/707/GSR-ACL-pub.shtml. 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 1.0 2001-November-14 08:00 UTC -0800 Initial public release 

Revision 1.1 2001-November-15 12:00 UTC -08:00 Update table with fixed IOS releases 





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/warp/public/707/sec_incident_response.shtml. This includes 

instructions for press inquiries regarding Cisco security notices. 



All Cisco Security Advisories are available at http://www.cisco.com/go/psirt 







--------------------------------------------------------------------------------



This notice is Copyright 2001 by Cisco Systems, Inc. This notice may be 

redistributed freely after the release date given at the top of the text, provided 

that redistributed copies are complete and unmodified, and include all date and 

version information. 





[***** End Cisco Security Advisory: Revision 1.1 *****]

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