Cisco Security Advisory: Vulnerability in Cisco IOS with OSPF, MPLS VPN, and Supervisor 32, Supervisor 720, or Route Switch Processor 720



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Cisco Security Advisory: Vulnerability in Cisco IOS with OSPF, MPLS
VPN, and Supervisor 32, Supervisor 720, or
Route Switch Processor 720

Advisory ID: cisco-sa-20080326-queue

http://www.cisco.com/warp/public/707/cisco-sa-20080326-queue.shtml

Revision 1.0

For Public Release 2008 March 26 1600 UTC (GMT)

Summary
=======

Certain Cisco Catalyst 6500 Series and Cisco 7600 Router devices that
run branches of Cisco IOS based on 12.2 can be vulnerable to a denial
of service vulnerability that can prevent any traffic from entering
an affected interface. For a device to be vulnerable, it must be
configured for Open Shortest Path First (OSPF) Sham-Link and Multi
Protocol Label Switching (MPLS) Virtual Private Networking (VPN).
This vulnerability only affects Cisco Catalyst 6500 Series or
Catalyst 7600 Series devices with the Supervisor Engine 32 (Sup32),
Supervisor Engine 720 (Sup720) or Route Switch Processor 720 (RSP720)
modules. The Supervisor 32, Supervisor 720, Supervisor 720-3B,
Supervisor 720-3BXL, Route Switch Processor 720, Route Switch
Processor 720-3C, and Route Switch Processor 720-3CXL are all
potentially vulnerable.

The OSPF and MPLS VPNs are not enabled by default.

This advisory is posted at
http://www.cisco.com/warp/public/707/cisco-sa-20080326-queue.shtml

Note: The March 26, 2008 publication includes five Security
Advisories. The Advisories all affect Cisco IOS. Each Advisory lists
the releases that correct the vulnerability described in the
Advisory, and the Advisories also detail the releases that correct
the vulnerabilities in all five Advisories. Please reference the
following software table to find a release which fixes all published
Security Advisories as of March 26th, 2008.

* March 26th bundled IOS Advisory Table
http://www.cisco.com/warp/public/707/cisco-sa-20080326-bundle.shtml

Individual publication links are listed below:

* Cisco IOS Virtual Private Dial-up Network Denial of Service
Vulnerability
http://www.cisco.com/warp/public/707/cisco-sa-20080326-pptp.shtml

* Multiple DLSw Denial of Service Vulnerabilities in Cisco IOS
http://www.cisco.com/warp/public/707/cisco-sa-20080326-dlsw.shtml

* Cisco IOS User Datagram Protocol Delivery Issue For IPv4/IPv6
Dual-stack Routers
http://www.cisco.com/warp/public/707/cisco-sa-20080326-IPv4IPv6.shtml

* Vulnerability in Cisco IOS with OSPF, MPLS VPN, and Supervisor
32, Supervisor 720, or Route Switch Processor 720
http://www.cisco.com/warp/public/707/cisco-sa-20080326-queue.shtml

* Cisco IOS Multicast Virtual Private Network (MVPN) Data Leak
http://www.cisco.com/warp/public/707/cisco-sa-20080326-mvpn.shtml


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

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

All Cisco products based on the Supervisor Engine 32 (Sup32),
Supervisor Engine 720 (Sup720) or Route Switch Processor 720 (RSP720)
are potentially vulnerable. Cisco Sup720 and RSP720 products have
support for daughter cards that enhance their functionality. These
daughter cards attach directly to the Sup720 or RSP720 and have names
like PFC-3B, PFC-3BXL, PFC-3C, and PFC-3CXL. The product number of
the Sup720 or RSP720 can change to reflect the daughter card that is
installed, such as RSP720-3CXL.

Because the vulnerability affects the Sup720 and RSP720, all versions
of the Sup720 or RSP720 are vulnerable, regardless of the daughter
card that is installed.

* Cisco Catalyst 6500 Series devices with the Sup32, Sup720,
Sup720-3B, or Sup720-3BXL
* Cisco 7600 Series devices with the Sup32, Sup720, Sup720-3B, or
Sup720-3BXL
* Cisco 7600 Series devices with the RSP720, RSP720-3C, or
RSP720-3CXL
* Cisco ME 6524 Ethernet Switch

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

No other Cisco products are currently known to be affected by this
vulnerability.

Cisco Bug ID CSCsf12082 was integrated into additional IOS releases
that do not run on the vulnerable hardware, but only the platforms
mentioned in the Vulnerable Products section above are affected by
this vulnerability.

Details
=======

Vulnerable Cisco devices, when configured for Multi Protocol Label
Switching (MPLS) Virtual Private Networking (VPN) and Open Shortest
Path First (OSPF) sham-link, can suffer from a blocked queue,
memory leak and/or restart of the device

This vulnerability is documented in Cisco bug ID CSCsf12082, and has
been assigned CVE ID CVE-2008-0057.

The following combination of hardware and software configuration must
be present for the device to be vulnerable:

* Cisco Catalyst Sup32, Sup720, or RSP720 is present
* MPLS VPN is configured
* OSPF sham-link is configured

In order to determine whether you are running this feature, use the
show running-config command and search for the address-family vpnv4
and area sham-link router configuration commands. The following
command displays all configuration lines that meet the following
criteria:

* Begins with the word "router," OR
* Includes "address-family vpnv4," OR
* Includes "sham-link"

Router# show run | include ^router |address-family vpnv4|sham-link
router bgp 1
address-family vpnv4
router ospf 1 vrf VRFNAME
area 0 sham-link 192.168.1.1 192.168.100.1
Router#

For customers that run versions of IOS that support the section
modifier, an additional option is available to view the relevant
sections of the running configuration:

Router# show run | section ^router
router bgp 1
[snip]
address-family vpnv4
router ospf 1 vrf VRFNAME
area 0 sham-link 192.168.1.1 192.168.100.1
[snip]

If certain packets are received by a device that meets the above
requirements, the input queue of the interface that receives these
packets can become blocked, which can prohibit additional traffic
from entering the interface and cause a denial of service condition.
In addition to a potential blocked interface queue, the device can
also suffer a memory leak or restart. In the event of a memory leak,
the device is unable to forward traffic once available memory is
depleted.

For more information on MPLS VPNs, please reference the following
document:

http://www.cisco.com/en/US/docs/net_mgmt/vpn_solutions_center/1.1/user/guide/VPN_UG1.html

For more information on OSPF sham-links, please reference the
following document:

http://www.cisco.com/en/US/docs/ios/12_2t/12_2t8/feature/guide/ospfshmk.html

Identifying a Memory Leak
+------------------------

This vulnerability can manifest as a leak in the I/O memory pool. The
following is an example of a system message that indicates an
exhaustion of the I/O pool:

006029: Aug 10: %SYS-2-MALLOCFAIL: Memory allocation of 808 bytes failed from 0x41613238, alignment 32
Pool: I/O Free: 176 Cause: Not enough free memory
Alternate Pool: None Free: 0 Cause: No Alternate pool

Note that in the above output, the affected memory pool is Pool: I/O,
and the cause is Cause: Not enough free memory. This output indicates
that the I/O memory pool has been exhausted.

Additionally, a user with enable-level access can check the device
through the show buffers command to identify buffer allocation
failures.

Router#show buffers
Buffer elements:
496 in free list (500 max allowed)
77298300 hits, 0 misses, 0 created

Public buffer pools:
Small buffers, 104 bytes (total 148654, permanent 1024, peak 148654 @ 1d12h):
0 in free list (128 min, 2048 max allowed)
24688031 hits, 4023203 misses, 0 trims, 147630 created
3243434 failures (3182828 no memory)

The above output shows that buffer allocation failed due to
insufficient memory.

Identifying a Blocked Interface
+------------------------------

A symptom of this type of blocked queue is the failure of
control-plane protocols such as routing protocols (OSPF, Enhanced
Interior Gateway Routing Protocol (EIGRP), Border Gateway Protocol
(BGP), Intermediate System to Intermediate System (ISIS), etc.) and
MPLS TDP/LDP to properly establish connections over an affected
interface.

In order to identify a blocked input interface, issue the show
interfaces command, and search for the Input Queue line. The size of
the input queue can continue to increase. If the current size, which
is 76 in the example below, is larger than the maximum size (75), the
input queue is blocked.

It is possible that a device receives a high rate of traffic destined
to the control plane, and the full queue is only a transient event.
In order to verify if the interface is actually blocked, shut down
the interface with the shutdown interface configuration command and
examine the input queue. If the input queue does not display 0
packets, the interface is blocked.

Router#show interface ethernet 0/0
Ethernet0/0 is up, line protocol is up
Hardware is AmdP2, address is 0050.500e.f1e0 (bia 0050.500e.f1e0)
Internet address is 172.16.1.9/24
MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, rely 255/255, load 1/255
Encapsulation ARPA, loopback not set, keepalive set (10 sec)
ARP type: ARPA, ARP Timeout 04:00:00
Last input 00:00:41, output 00:00:07, output hang never
Last clearing of "show interface" counters 00:07:18
Input queue: 76/75/1091/0 (size/max/drops/flushes); Total output drops: 0


!--- The 76/75 shows that this is blocked


Vulnerability Scoring Details
=============================

Cisco has provided scores for the vulnerabilities in this advisory
based on the Common Vulnerability Scoring System (CVSS). The CVSS
scoring in this Security Advisory is done in accordance with CVSS
Version 2.0.

CVSS is a standards-based scoring method that conveys vulnerability
severity and helps determine urgency and priority of response.

Cisco has provided a base and temporal score. Customers can then
compute environmental scores to assist in determining the impact of
the vulnerability in individual networks.

Cisco has provided an FAQ to answer additional questions regarding
CVSS at
http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html

Cisco has also provided a CVSS calculator to help compute the
environmental impact for individual networks at
http://intellishield.cisco.com/security/alertmanager/cvss

CSCsf12082 - SUP720 facing small buffer leak and crashes

CVSS Base Score - 7.8

Access Vector: Network
Access Complexity: Low
Authentication: None

Confidentiality Impact: None
Integrity Impact: None
Availability Impact: Complete

CVSS Temporal Score - 6.1

Exploitability: Proof-of-Concept
Remediation Level: Official-Fix
Report Confidence: Confirmed

Impact
======

Exploitation of this vulnerability may result in a blocked interface
input queue, memory leak, and/or restart of the device. Repeated
exploitation of this vulnerability may result in an extended denial
of service.

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

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) names a Cisco IOS
release train. If a given release train is vulnerable, then the
earliest possible releases that contain the fix (along with the
anticipated date of availability for each, if applicable) are listed
in the "First Fixed Release" column of the table. The "Recommended
Release" column indicates the releases which have fixes for all the
published vulnerabilities at the time of this Advisory. 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. Cisco recommends upgrading to a release equal to or
later than the release in the "Recommended Releases" column of the
table.

+----------------------------------------+
| Major | Availability of Repaired |
| Release | Releases |
|------------+---------------------------|
| Affected | First Fixed | Recommended |
| 12.0-Based | Release | Release |
| Releases | | |
|----------------------------------------|
| There are no affected 12.0 based |
| releases |
|----------------------------------------|
| Affected | First Fixed | Recommended |
| 12.1-Based | Release | Release |
| Releases | | |
|----------------------------------------|
| There are no affected 12.1 based |
| releases |
|----------------------------------------|
| Affected | First Fixed | Recommended |
| 12.2-Based | Release | Release |
| Releases | | |
|------------+-------------+-------------|
| 12.2 | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2B | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2BC | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2BW | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2BY | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2BZ | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2CX | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2CY | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2CZ | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2DA | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2DD | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2DX | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2EU | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2EW | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2EWA | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2EX | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2EY | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2EZ | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2FX | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2FY | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2FZ | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2IXA | Vulnerable; | |
| | contact TAC | |
|------------+-------------+-------------|
| 12.2IXB | Vulnerable; | |
| | contact TAC | |
|------------+-------------+-------------|
| 12.2IXC | Vulnerable; | |
| | contact TAC | |
|------------+-------------+-------------|
| 12.2IXD | Vulnerable; | |
| | contact TAC | |
|------------+-------------+-------------|
| | Vulnerable; | 12.2(18) |
| | migrate to | IXF; |
| 12.2IXE | any release | Available |
| | in 12.2IXF | on |
| | | 31-MAR-2008 |
|------------+-------------+-------------|
| 12.2JA | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2JK | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2MB | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2MC | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2S | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SB | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SBC | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SCA | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SE | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SEA | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SEB | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SEC | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SED | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SEE | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SEF | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SEG | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SG | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SGA | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SL | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SM | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SO | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SRA | 12.2(33) | 12.2(33) |
| | SRA4 | SRA7 |
|------------+-------------+-------------|
| 12.2SRB | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SRC | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SU | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SV | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SVA | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SVC | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SVD | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SW | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SX | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| | Vulnerable; | 12.2(18) |
| 12.2SXA | first fixed | SXF13 |
| | in 12.2SXF | |
|------------+-------------+-------------|
| | Vulnerable; | 12.2(18) |
| 12.2SXB | first fixed | SXF13 |
| | in 12.2SXF | |
|------------+-------------+-------------|
| | Vulnerable; | 12.2(18) |
| 12.2SXD | first fixed | SXF13 |
| | in 12.2SXF | |
|------------+-------------+-------------|
| | Vulnerable; | 12.2(18) |
| 12.2SXE | first fixed | SXF13 |
| | in 12.2SXF | |
|------------+-------------+-------------|
| 12.2SXF | 12.2(18) | 12.2(18) |
| | SXF6 | SXF13 |
|------------+-------------+-------------|
| 12.2SXH | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SY | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2SZ | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2T | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2TPC | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2UZ | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XA | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XB | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XC | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XD | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XE | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XF | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XG | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XH | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XI | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XJ | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XK | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XL | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XM | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XN | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XO | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XQ | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XR | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XS | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XT | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XU | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XV | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2XW | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YA | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YB | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YC | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YD | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YE | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YF | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YG | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YH | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YJ | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YK | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YL | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YM | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YN | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YO | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YP | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YQ | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YR | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YS | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YT | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YU | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YV | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YW | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YX | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YY | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2YZ | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2ZA | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2ZB | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2ZC | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2ZD | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2ZE | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2ZF | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2ZG | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2ZH | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2ZJ | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2ZL | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| 12.2ZP | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| | Vulnerable; | |
| 12.2ZU | migrate to | 12.2(33) |
| | any release | SXH2 |
| | in 12.2SXH | |
|------------+-------------+-------------|
| 12.2ZY | Not | |
| | Vulnerable | |
|------------+-------------+-------------|
| Affected | First Fixed | Recommended |
| 12.3-Based | Release | Release |
| Releases | | |
|----------------------------------------|
| There are no affected 12.3 based |
| releases |
|----------------------------------------|
| Affected | First Fixed | Recommended |
| 12.4-Based | Release | Release |
| Releases | | |
|----------------------------------------|
| There are no affected 12.4 based |
| releases |
+----------------------------------------+

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

Once a device interface queue has been exhausted, only a device
restart can clear OSPF packets in the blocked queue.

Due to the manner in which these packets are processed, the queue
block occurs prior to the OSPF MD5 check. The OSPF MD5 configuration
does not protect a device from this vulnerability.

Increasing the Selective Packet Discard (SPD) Headroom
+-----------------------------------------------------

At the most basic level, the Selective Packet Discard (SPD) provides
extended buffering for control plane traffic. Known as the SPD
headroom, this additional queue depth is typically reserved for
traffic with IP Precedence equal to 6 (such as BGP), the
Connectionless Network Service (CLNS) based routing protocol
Intermediate System-to-Intermediate System (IS-IS), OSPF, and Layer 2
keepalives.

Increasing the SPD headroom provides additional buffering for OSPF
packets. In the event of a blocked queue, the SPD headroom can be
increased to allow more control plane traffic buffer space.

More information on SPD can be found in the following white paper:

http://www.cisco.com/web/about/security/intelligence/spd.html

It is possible to expand the queue size to accommodate more packets,
but packets can still accumulate until the expanded queue is
exhausted. As a temporary workaround that allows traffic to continue
to flow, the input hold queue can be increased. Any additional
malformed packets still fill the queue, but increasing the input
queue depth can extend the amount of time before the input queue
fills and traffic ceases flowing. The following example demonstrates
how to set the input queue size from the default of 75 to the maximum
of 4096:

Router# configure terminal
Router(configure)# interface FastEthernet 0/0
Router(config-if)# hold-queue 4096 in

Removing OSPF Sham-Link Configuration
+------------------------------------

Because OSPF Sham-Link configuration is required for the
vulnerability to be present, removing Sham-Link functionality
eliminates exposure to this vulnerability. In order to remove the
OSPF Sham-Link configuration from a device, the OSPF configuration
must be changed on each interface where Sham-Link is configured.

For configuration information on OSPF Sham-Link, please consult the
following document:

http://www.cisco.com/en/US/docs/ios/12_2t/12_2t8/feature/guide/ospfshmk.html

Cisco IOS Embedded Event Manager
+-------------------------------

Cisco IOS Embedded Event Manager (EEM) provides event detection and
reaction capabilities on a Cisco IOS device. It is possible to detect
blocked interface queues with an EEM policy. EEM can alert
administrators of blocked interfaces with email, a syslog message, or
a Simple Network Management Protocol (SNMP) trap.

A sample EEM policy that uses syslog to alert administrators of
blocked interfaces is available at Cisco Beyond, an online community
dedicated to EEM. A sample script is available at the following link:

http://forums.cisco.com/eforum/servlet/EEM?page=eem&fn=script&scriptId=981

More information about EEM is available from Cisco.com at the
following link:

http://www.cisco.com/en/US/products/ps6815/products_ios_protocol_group_home.html

Obtaining Fixed Software
========================

Cisco has released free software updates that address this
vulnerability. 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/en/US/products/prod_warranties_item09186a008088e31f.html
or as otherwise set forth at Cisco.com Downloads at
http://www.cisco.com/public/sw-center/sw-usingswc.shtml.

Do not contact 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 agreements 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 do not hold a Cisco
service contract, and customers who purchase through third-party
vendors but are unsuccessful in obtaining fixed software through
their point of sale should acquire 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

Customers should have their product serial number available and be
prepared to give the URL of this notice as evidence of 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 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 reported to Cisco by a customer.

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-20080326-queue.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 | 2008-March-26 | 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.
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