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Cisco Security Advisory: ICMP Unreachable vulnerability in Cisco 12000
Series
Internet Router
Revision 1.0
For Public Release 2001 November 14 08:00 (UTC -0800)
_________________________________________________________________
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 a heavy network scanning. This
vulnerability is tracked by three different bug IDs: CSCdr46528,
CSCdt66560, CSCds36541. 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 Internet
Control Message Protocol (ICMPs) unreachables at all or to rate limit
them.
This advisory is available at
http://www.cisco.com/warp/public/707/GSR-unreachables-pub.shtml
Affected Products
Only Cisco 12000 Series Internet Routers are affected with this
vulnerability. No other routers or switches are affected. Not all line
cards of a 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 "sh diag" command while in enable mode.
The engine type will be displayed as "L3 Engine: x" where x will be
the correspoding 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]
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 IOSŪ release is vulnerable to
a particular issue:
+--------------+------------------+------------------+--------------+
| DDTS | 12.0S | 12.0SC | 12.0ST |
+--------------+------------------+------------------+--------------+
| CSCdr46528 | Vulnerable | | Vulnerable |
+--------------+------------------+------------------+--------------+
| CSCds36541 | Vulnerable | Vulnerable | Vulnerable |
+--------------+------------------+------------------+--------------+
| CSCdt66560 | Vulnerable | | Vulnerable |
+--------------+------------------+------------------+--------------+
Details
The received packet will be dropped when either there is no valid path
to the destination or when the packet should be routerd 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 networks default path,
or from a direct Denial of Service (DOS) against the router. For
further information of "Black Hole" filtering consult the document:
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 1 Engine 2 Engine 4|
+------------+---------------+--------------+----------------+---------+
|CSCdr46528 | Vulnerable | | | |
+------------+---------------+--------------+----------------+---------+
|CSCds36541 | | Vulnerable | | |
+------------+---------------+--------------+----------------+---------+
|CSCdt66560 | | | Vulnerable | |
+------------+---------------+--------------+----------------+---------+
Impact
Exploitation of this 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
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. Interims 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 CSCdr46528 | Rebuild | Interim** | Maintenance|
+-------+------------------------+-------------+------------+------------+
| 12.0S |Core/ISP support: GSR, |12.0(16)S1 |12.0(16.5)S | 12.0(17)S |
| |RSP, c7200 | | | |
| |Cisco IOS software | | | |
| |Release 12.OST is an | | | |
| |early deployment (ED) | | | |
+-------+------------------------+-------------+------------+------------+
|12.0ST |release for the Cisco |12.0(15.6)ST3|12.0(16.5)ST| 12.0(17)ST |
| |7200, 7500/7000RSP and | | | |
| |12000 (GSR) series | | | |
| |routers for Service | | | |
| |Providers (ISPs). | | | |
+-------+------------------------+-------------+------------+------------+
| Vulnerability CSCds36541 | Rebuild | Interim** | Maintenance|
+-------+------------------------+-------------+------------+------------+
| 12.0S |Core/ISP support: GSR, |12.0(13.6)S2 |12.0(14.1)S | 12.0(15)S |
| |RSP, c7200 | | | |
+-------+------------------------+-------------+------------+------------+
|12.0SC |Cable/broadband ISP: |12.0(13.6)SC1|12.0(14.6)SC| 12.0(15)SC |
| |ubr7200 | | | |
| |Cisco IOS software | | | |
| |Release 12.OST is an | | | |
| |early deployment (ED) | | | |
+-------+------------------------+-------------+------------+------------+
|12.0ST |release for the Cisco | |12.0(14.3)ST| |
| |7200, 7500/7000RSP and | | | |
| |12000 (GSR) series | | | |
| |routers for Service | | | |
| |Providers (ISPs). | | | |
+-------+------------------------+-------------+------------+------------+
| Vulnerability CSCdt66560 | Rebuild | Interim** | Maintenance|
+-------+------------------------+-------------+------------+------------+
| 12.0S |Core/ISP support: GSR, |12.0(16)S1 |12.0(16.6)S | 12.0(17)S |
| |RSP, c7200 | | | |
| |Cisco IOS software | | | |
| |Release 12.OST is an | | | |
| |early deployment (ED) | | | |
+-------+------------------------+-------------+------------+------------+
|12.0ST |release for the Cisco |12.0(15.6)ST3|12.0(16.6)ST| 12.0(17)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: 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
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 sould be
applied on an interface, like 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 ureachable packets. The default value is 500. That menas that one
ICMP unreachable packet is send every 500 ms.
Exploitation and Public Announcements
The Cisco PSIRT is aware that some ISPs have experiencing difficulties
due to this vulnerability.
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-unreachables-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-20 08:00 GMT -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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