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Cisco Security Advisory: Multiple Vulnerabilities in Access Control List
Implementation for Cisco 12000 Series Internet Router
Revision 1.0
For Public Release 2001 November 14 08:00 (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
(http://www.cisco.com/warp/public/105/acl_wp.html).
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 (http://www.cisco.com/warp/public/105/acl_wp.html).
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 | Availability of Fixed Releases* |
| | Platform | |
+-------+------------------------+-------------+-------------+------------+
| Vulnerability CSCdm4476 | Rebuild | Interim** |Maintenance |
+-------+------------------------+-------------+-------------+------------+
| 12.0S |Core/ISP support: GSR, | |12.0(10.1)S | |
| |RSP, c7200 | | | |
+-------+------------------------+-------------+-------------+------------+
| Vulnerability CSCdu57417 | Rebuild | Interim** |Maintenance |
+-------+------------------------+-------------+-------------+------------+
| 12.0S |Core/ISP support: GSR, | |12.0(19.3)S |12.0(19)S |
| |RSP, c7200 | | | |
+-------+------------------------+-------------+-------------+------------+
| |Early deployment (ED) | | | |
| |release for the Cisco | | | |
|12.0ST |7200, 7500/7000RSP and |12.0(18.6)ST1|12.0(19.3)ST | |
| |12000 series routers | | | |
| |for Service Providers | | | |
| |(ISPs). | | | |
+-------+------------------------+-------------+-------------+------------+
| Vulnerability CSCdu03323 | Rebuild | Interim** |Maintenance |
+-------+------------------------+-------------+-------------+------------+
| 12.0S |Core/ISP support: GSR, |12.0(16)S2 |12.0(17.5)S |12.0(17)S |
| |RSP, c7200 | | | |
+-------+------------------------+-------------+-------------+------------+
| |Early deployment (ED) | | | |
| |release for the Cisco | | | |
|12.0ST |7200, 7500/7000RSP and |12.0(16.6)ST1|12.0(17.5)ST | |
| |12000 series routers | | | |
| |for Service Providers | | | |
| |(ISPs). | | | |
+-------+------------------------+-------------+-------------+------------+
| Vulnerability CSCdu35175 | Rebuild | Interim** |Maintenance |
+-------+------------------------+-------------+-------------+------------+
| 12.0S |Core/ISP support: GSR, | |12.0(19.6)S | |
| |RSP, c7200 | | | |
+-------+------------------------+-------------+-------------+------------+
| |Early deployment (ED) | | | |
| |release for the Cisco | | | |
|12.0ST |7200, 7500/7000RSP and | |12.0(19.6)ST | |
| |12000 series routers | | | |
| |for Service Providers | | | |
| |(ISPs). | | | |
+-------+------------------------+-------------+-------------+------------+
| Vulnerability CSCdt96370 | Rebuild | Interim** |Maintenance |
+-------+------------------------+-------------+-------------+------------+
| 12.0S |Core/ISP support: GSR, |12.0(16)S1 |12.0(17.1)S |12.0(18)S |
| |RSP, c7200 | | | |
+-------+------------------------+-------------+-------------+------------+
| |Early deployment (ED) | | | |
|12.0ST |release for the Cisco |12.0(15.6)ST3|12.0(17.1)ST |12.0(18)ST |
| |7200, 7500/7000RSP and | | | |
| |12000 (GSR) series | | | |
| |routers for Service | | | |
| |Providers (ISPs). | | | |
+-------+------------------------+-------------+-------------+------------+
| Vulnerability CSCdt69741 | Rebuild | Interim** |Maintenance |
+-------+------------------------+-------------+-------------+------------+
| 12.0S |Core/ISP support: GSR, |12.0(16.6)S2 |12.0(17.3)S |12.0(18)S |
| |RSP, c7200 | | | |
+-------+------------------------+-------------+-------------+------------+
| |Early deployment (ED) | | | |
|12.0ST |release for the Cisco | |12.0(17.3)ST |12.0(18)ST |
| |7200, 7500/7000RSP and | | | |
| |12000 (GSR) series | | | |
| |routers for Service | | | |
| |Providers (ISPs). | | | |
+-------+------------------------+-------------+-------------+------------+
| 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: tacat_private
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 "psirtat_private" or
"security-alertat_private" 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-announceat_private
* bugtraqat_private
* first-teamsat_private (includes CERT/CC)
* ciscoat_private
* comp.dcom.sys.cisco
* firewallsat_private
* 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
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.
_________________________________________________________________
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