[VulnWatch] Cisco Security Advisory: IOS Stack Group Bidding Protocol Crafted Packet DoS



-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Cisco Security Advisory: IOS Stack Group Bidding Protocol Crafted
Packet DoS

Document ID: 68793

Advisory ID: cisco-sa-20060118-sgbp

http://www.cisco.com/warp/public/707/cisco-sa-20060118-sgbp.shtml

Revision 1.0
============

For Public Release 2006 January 18 1600 UTC (GMT)

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

Contents
========

Summary
Affected Products
Details
Impact
Software Versions and Fixes
Workarounds
Obtaining Fixed Software
Exploitation and Public Announcements
Status of This Notice: FINAL
Distribution
Revision History
Cisco Security Procedures

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

Summary
=======

The Cisco IOS Stack Group Bidding Protocol (SGBP) feature in certain
versions of Cisco IOS software is vulnerable to a
remotely-exploitable denial of service condition. Devices that do not
support or have not enabled the SGBP protocol are not affected by
this vulnerability.

Cisco has made free software available to address this vulnerability
for affected customers. There are workarounds available to mitigate
the effects of the vulnerability.

This advisory is posted at
http://www.cisco.com/warp/public/707/cisco-sa-20060118-sgbp.shtml

Affected Products
=================

Vulnerable Products
+------------------

This vulnerability affects any device that runs Cisco IOS and has
enabled the SGBP protocol. SGBP is enabled by defining a stack group,
which is done using the global IOS command "sgbp group <name>". The
presence of this command will cause the device to begin listening on
port 9900, even if the remaining SGBP parameters are not fully
configured.

The following examples demonstrate device configurations for which
SGBP is enabled:

Router#show sgbp
Group Name: test Ref: 0xA3728C00
Seed bid: default, 50, default seed bid setting

Or:

Router#show running-config | include sgbp
sgbp group test_group

If your device displays output similar to either of the above
examples, please consult the IOS software table below to determine
whether your version of IOS is affected.

Products Confirmed Not Vulnerable
+--------------------------------

Cisco products that do not run IOS, do not contain support for SGBP,
or do not have SGBP enabled are not affected by this vulnerability.

Systems on which SGBP is not supported or enabled will return either
blank output or an error message. The following examples demonstrate
device configurations that are not affected by this vulnerability:

* A system that supports but is not enabled for SGBP returns this
output:

Router#show sgbp
Router#

* A system that does not support SGBP returns this error message:

Router#show sgbp
Router#show sgbp
^
% Invalid input detected at '^' marker.

Details
=======

Multilink PPP (MLP) allows users to combine multiple PPP links into a
single logical network connection, thus enabling on demand bandwidth
allocation. When implemented across multiple device chassis, this is
known as Multichassis Multilink PPP (MMP). The Stack Group Bidding
Protocol is the mechanism by which devices participating in MMP
locate each other and negotiate for a connection termination point.

The SGBP implementation provided by the Cisco Internetwork Operating
System (IOS) is susceptible to a denial of service attack when
presented with a crafted UDP packet. Sending such a packet to port
9900 of an affected device will cause it to freeze and stop
responding to or passing traffic. After a delay, the system watchdog
timer will detect this condition and force a reset of the device. The
system recovery behavior will be controlled by the device
configuration register; for example, the router may reload or drop to
the ROM monitor.

This vulnerability is documented in Cisco bug ID CSCsb11124.

Impact
======

Successful exploitation of this vulnerability may cause the affected
device to become unresponsive and trigger a hardware reset, resulting
in a denial of service condition.

Software Versions and Fixes
===========================

Cisco has provided updated software to address this vulnerability.
For further details, please refer to the software table below.

When considering software upgrades, also consult
http://www.cisco.com/go/psirt
and any subsequent advisories to determine exposure and a complete
upgrade solution.

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 Technical Assistance Center ("TAC") or your contracted
maintenance provider for assistance.

Each row of the Cisco IOS software table (below) 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 (the "First Fixed Release") and the
anticipated date of availability for each are listed in the "Rebuild"
and "Maintenance" columns. A device running a release in the given
train that is earlier than the release in a specific column (less
than the First Fixed Release) is known to be vulnerable. The release
should be upgraded at least to the indicated release or a later
version (greater than or equal to the First Fixed Release label).

For more information on the terms "Rebuild" and "Maintenance,"
consult the following URL:
http://www.cisco.com/warp/public/620/1.html

+----------------------------------------+
| Major | Availability of Repaired |
| Release | Releases |
|------------+---------------------------|
| Affected | | |
| 12.0-Based | Rebuild | Maintenance |
| Release | | |
|------------+---------------------------|
| 12.0 | Migrate to 12.2(32) |
|------------+---------------------------|
| | 12.0(28)S6 | |
| |-------------+-------------|
| | 12.0(30)S5; | |
| | available | |
| | 23-Feb-06 | |
| |-------------+-------------|
| 12.0S | 12.0(31)S3; | |
| | available | |
| | 26-Jan-06 | |
| |-------------+-------------|
| | | 12.0(32)S; |
| | | available |
| | | 26-Jan-06 |
|------------+---------------------------|
| 12.0SC | Migrate to 12.3(13a)BC or |
| | later |
|------------+---------------------------|
| 12.0T | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.0XA | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.0XC | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.0XD | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.0XE | Migrate to 12.1(26)E5 |
|------------+---------------------------|
| 12.0XG | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.0XH | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.0XI | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.0XJ | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.0XK | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.0XL | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.0XN | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.0XR | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| Affected | | |
| 12.1-Based | Rebuild | Maintenance |
| Release | | |
|------------+---------------------------|
| 12.1 | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.1AA | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.1E | 12.1(26)E5 | |
|------------+---------------------------|
| 12.1EC | Migrate to 12.3(13a)BC or |
| | later |
|------------+---------------------------|
| 12.1EX | Migrate to 12.1(26)E5 |
|------------+---------------------------|
| 12.1EZ | Migrate to 12.1(26)E5 |
|------------+---------------------------|
| 12.1GA | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.1GB | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.1T | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.1XA | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.1XD | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.1XH | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.1XI | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.1XL | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.1XM | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.1XQ | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.1XS | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.1XU | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.1XW | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.1XX | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.1XY | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.1XZ | Migrate to 12.2(32) or |
| | later |
|------------+---------------------------|
| 12.1YA | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.1YB | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.1YD | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| Affected | | |
| 12.2-Based | Rebuild | Maintenance |
| Release | | |
|------------+-------------+-------------|
| 12.2 | | 12.2(32) |
|------------+---------------------------|
| 12.2B | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| 12.2BC | Migrate to 12.3(13a)BC or |
| | later |
|------------+---------------------------|
| 12.2BW | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.2BY | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| 12.2CX | Migrate to 12.3(13a)BC or |
| | later |
|------------+---------------------------|
| 12.2DD | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| 12.2DX | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| 12.2MC | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| | 12.2(14) | |
| | S16; | |
| | available | |
| | 9-Feb-06 | |
| 12.2S | | |
| | 12.2(18)S | |
| | and later | |
| | are not | |
| | vulnerable. | |
|------------+---------------------------|
| 12.2SU | Migrate to 12.3(14)T6 |
|------------+---------------------------|
| 12.2SY | Migrate to 12.2SXD or |
| | later |
|------------+---------------------------|
| 12.2SZ | Migrate to 12.2S or later |
|------------+---------------------------|
| 12.2T | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.2XA | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.2XB | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.2XC | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| 12.2XF | Migrate to 12.3(13a)BC or |
| | later |
|------------+---------------------------|
| 12.2XG | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.2XK | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.2XL | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.2XS | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.2XT | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.2XV | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.2YD | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| 12.2YE | Migrate to 12.2S or later |
|------------+---------------------------|
| 12.2YN | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| 12.2YT | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.2YW | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| 12.2YX | Migrate to 12.3(14)T6 |
|------------+---------------------------|
| 12.2YY | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| 12.2YZ | Migrate to 12.2S or later |
|------------+---------------------------|
| 12.2ZA | Migrate to 12.2SXD or |
| | later |
|------------+---------------------------|
| 12.2ZB | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| 12.2ZD | Contact TAC |
|------------+---------------------------|
| 12.2ZE | Migrate to 12.3(16) or |
| | later |
|------------+---------------------------|
| 12.2ZJ | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| 12.2ZN | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| Affected | | |
| 12.3-Based | Rebuild | Maintenance |
| Release | | |
|------------+-------------+-------------|
| 12.3 | | 12.3(16) |
|------------+---------------------------|
| 12.3B | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| 12.3BC | | 12.3(13a)BC |
|------------+---------------------------|
| 12.3BW | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| | 12.3(11)T9 | |
|12.3T |-------------+-------------|
| | 12.3(14)T6 | |
|------------+---------------------------|
| 12.3XB | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| 12.3XD | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| 12.3XF | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| 12.3XH | Migrate to 12.3(11)T9 or |
| | later |
|------------+---------------------------|
| 12.3XI | Contact TAC |
|------------+---------------------------|
| 12.3XJ | Migrate to 12.3(14)YX or |
| | later |
|------------+---------------------------|
| 12.3XM | Migrate to 12.3(14)T6 |
|------------+---------------------------|
| 12.3XQ | Migrate to 12.4(3) or |
| | later |
|------------+---------------------------|
| 12.3XU | Migrate to 12.4(4)T or |
| | later |
|------------+---------------------------|
| 12.3XW | Migrate to 12.3(14)YX or |
| | later |
|------------+---------------------------|
| 12.3YF | Migrate to 12.3(14)YX or |
| | later |
|------------+---------------------------|
| 12.3YG | Contact TAC |
|------------+---------------------------|
| 12.3YJ | Migrate to 12.3(14)YQ2 |
|------------+---------------------------|
| 12.3YK | Contact TAC |
|------------+---------------------------|
| 12.3YM | 12.3(14)YM4 | |
|------------+-------------+-------------|
| 12.3YQ | 12.3(14)YQ2 | |
|------------+---------------------------|
| 12.3YT | Contact TAC |
|------------+---------------------------|
| 12.3YU | Contact TAC |
|------------+---------------------------|
| 12.3YX | | 12.3(14)YX |
|------------+-------------+-------------|
| Affected | | |
| 12.4-Based | Rebuild | Maintenance |
| Release | | |
|------------+-------------+-------------|
| | 12.4(1b) | |
|12.4 |-------------+-------------|
| | | 12.4(3) |
|------------+-------------+-------------|
| 12.4MR | | 12.4(4)MR |
|------------+-------------+-------------|
| | 12.4(2)T3 | |
|12.4T |-------------+-------------|
| | | 12.4(4)T |
|------------+-------------+-------------|
| 12.4XA | | 12.4(2)XA |
|------------+-------------+-------------|
| 12.4XB | | 12.4(2)XB |
+----------------------------------------+

Workarounds
===========

* Configure Access Control Lists (ACLs)

For sites that require the SGBP protocol to be enabled, it may be
possible to apply Access Control Lists (ACLs) to prevent
untrusted hosts from exploiting this vulnerability. The following
extended access-list can be adapted to your network. This example
assumes that the SGBP members communicate using the 192.168.10.0
network.

access-list 101 permit udp 192.168.10.0 0.0.0.255 192.168.10.0
0.0.0.255 port eq 9900
access-list 101 deny udp any 192.168.10.0 0.0.0.255 port eq
9900
access-list 101 permit ip any any

The access-list must then be applied to all interfaces using
configuration commands such as:

interface ethernet 0/0
ip access-group 101 in

* Enable Control Plane Policing

The Control Plane Policy (CoPP) feature may be used to mitigate
this vulnerability, as in this example:

! Do not police SGBP traffic from the trusted network
access-list 140 deny udp 192.168.10.0 0.0.0.255 any eq 9900
! Police SGBP traffic from untrusted hosts and networks
access-list 140 permit udp any any eq 9900
! Do not police any other type of traffic going to the router
access-list 140 deny ip any any
!
class-map match-all sgbp-class
match access-group 140
!
policy-map control-plane-policy
! Drop all traffic that matches the class "sgbp-class"
class sgbp-class
drop
!
control-plane
service-policy input control-plane-policy

Note: CoPP is only available on certain platforms and IOS release
trains. Additional information on the configuration and use of
the CoPP feature can be found at the following URL:
http://www.cisco.com/en/US/products/sw/iosswrel/ps1838/
products_white_paper09186a0080211f39.shtml

* Infrastructure ACLs (iACL)

Although it is often difficult to block traffic transiting your
network, it is possible to identify traffic which should never be
allowed to target your infrastructure devices and block that
traffic at the border of your network. Infrastructure ACLs are
considered a network security best practice and should be
considered as a long-term addition to good network security as
well as a workaround for this specific vulnerability. The white
paper entitled "Protecting Your Core: Infrastructure Protection
Access Control Lists" presents guidelines and recommended
deployment techniques for iACLs:
http://www.cisco.com/warp/public/707/iacl.html

* Configuring Receive Access Lists (rACLs)

For distributed platforms, rACLs may be an option starting in
Cisco IOS Software Versions 12.0(21)S2 for the 12000 series GSR
and 12.0(24)S for the 7500 series. The receive access lists
protect the device from harmful traffic before the traffic can
impact the route processor. Receive path ACLs are considered a
network security best practice, and should be considered as a
long-term addition to good network security, as well as a
workaround for this specific vulnerability. The CPU load is
distributed to the line card processors and helps mitigate load
on the main route processor. The white paper entitled "GSR:
Receive Access Control Lists" will help identify and allow
legitimate traffic to your device and deny all unwanted packets:
http://www.cisco.com/warp/public/707/racl.html

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@xxxxxxxxx" or "security-alert@xxxxxxxxx"
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@xxxxxxxxx

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 vulnerability described in this advisory.

This vulnerability was discovered during internal testing.

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 advisory is posted on Cisco's worldwide website at
http://www.cisco.com/warp/public/707/cisco-sa-20060118-sgbp.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@xxxxxxxxx
* first-teams@xxxxxxxxx
* bugtraq@xxxxxxxxxxxxxxxxx
* vulnwatch@xxxxxxxxxxxxx
* cisco@xxxxxxxxxxxxxxxxx
* cisco-nsp@xxxxxxxxxxxxxxx
* full-disclosure@xxxxxxxxxxxxxxxxx
* comp.dcom.sys.cisco@xxxxxxxxxxxxxxxxxx

Future updates of this advisory, if any, will be placed on Cisco's
worldwide website, but may or may not be actively announced on
mailing lists or newsgroups. Users concerned about this problem are
encouraged to check the above URL for any updates.

Revision History
================

+---------------------------------------+
| Revision | | Initial |
| 1.0 | 2006-January-18 | 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 website at
http://www.cisco.com/en/US/products/products_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

- -----------------------------------------------------------------------
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.0 (SunOS)

iD8DBQFDzm47ezGozzK2tZARAmLxAKDYI8fIszCIrKEPbtnxG5A/3zcS6QCfS0FC
vB8TjPqap9cvnRRPrpNWrQ4=
=BpZb
-----END PGP SIGNATURE-----