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Date: Wednesday, 18 June 2008 11:30:00 -0500 
From: Cisco Systems Product Security Incident Response Team <>
Subject: Cisco Security Advisory: Cisco Intrusion Prevention System Jumbo Frame Denial of Service

Hash: SHA1

Cisco Security Advisory: Cisco Intrusion Prevention System Jumbo
                         Frame Denial of Service

Advisory ID: cisco-sa-20080618-ips

Revision 1.0

For Public Release 2008 June 18 1600 UTC (GMT)



Cisco Intrusion Prevention System (IPS) platforms that have gigabit
network interfaces installed and are deployed in inline mode contain
a denial of service vulnerability in the handling of jumbo Ethernet
frames. This vulnerability may lead to a kernel panic that requires a
power cycle to recover platform operation. Platforms deployed in
promiscuous mode only or that do not contain gigabit network
interfaces are not vulnerable.

Cisco has released free software updates that address this
vulnerability. There is a workaround for this vulnerability.

This advisory is posted at

Affected Products

Vulnerable Products

The following Cisco IPS versions are affected:

  * Cisco Intrusion Prevention System version 5.x prior to 5.1(8)E2
  * Cisco Intrusion Prevention System version 6.x prior to 6.0(5)E2

The following Cisco IPS platforms ship with gigabit network
interfaces and are vulnerable if they are deployed in inline mode:

  * 4235
  * 4240
  * 4250
  * 4250SX *
  * 4250TX
  * 4250XL *
  * 4255
  * 4260
  * 4270

* The 4250SX and 4250XL models ship with gigabit network interfaces
that are normally used for remote administration and monitoring. If
the gigabit network interfaces are configured for use with inline
mode, the platform is vulnerable.

To determine the version of software that is running on a Cisco IPS
platform, log into the platform using the console or Secure Shell
(SSH) and issue the show version command.

    sensor# show version 
    Application Partition:
    Cisco Intrusion Prevention System, Version 6.0(4a)E1

To determine whether a Cisco IPS platform has interfaces configured
for inline mode, log into the platform using the console or SSH and
issue the show interfaces command. Look for paired interfaces in the
Inline Mode statement of the command output.

    sensor# show interfaces
    MAC statistics from interface GigabitEthernet0/1
       Interface function = Sensing interface
       Description =
       Media Type = TX
       Missed Packet Percentage = 0
       Inline Mode = Paired with interface GigabitEthernet0/0
    MAC statistics from interface GigabitEthernet0/0
       Interface function = Sensing interface
       Description =
       Media Type = TX
       Missed Packet Percentage = 0
       Inline Mode = Paired with interface GigabitEthernet0/1

Products Confirmed Not Vulnerable

The following Cisco IPS platforms are not vulnerable:

  * 4210
  * 4215
  * SSM-AIP10
  * SSM-AIP20
  * SSM-AIP40
  * IDSM2

Cisco IPS version 6.1(1) is not vulnerable. Cisco IOS with the
Intrusion Prevention System feature is not vulnerable. No other Cisco
products are currently known to be affected by this vulnerability.


Certain Cisco IPS platforms contain a denial of service vulnerability
in the handling of jumbo ethernet frames. When a specific series of
jumbo Ethernet frames is received on a gigabit network interface of a
vulnerable Cisco IPS platform that is deployed in inline mode, a
kernel panic may occur that results in the complete failure of the
platform and causes a network denial of service condition. Cisco IPS
platforms that are deployed in promiscuous mode only or that do not
contain gigabit network interfaces are not vulnerable.

Jumbo Ethernet support is usually deployed in data center
environments to increase inter-server communication performance and
is not a default configuration for Cisco routers and switches.
Support for jumbo Ethernet frames must be enabled on each device that
require the feature. In order to exploit this vulnerability, an
attacker must be able to inject jumbo Ethernet frames to a vulnerable
Cisco IPS platform that is deployed in inline mode.

If they are configured to use bypass mode to allow traffic to pass in
the event of a system failure, all Cisco IPS platforms will fail to
forward traffic except for the 4260 and 4270 platforms. The Cisco IPS
4260 and 4270 platforms contain a hardware bypass feature that allows
them to pass network traffic in the event of a kernel panic or power
outage. They will pass traffic by default if the hardware bypass
feature is engaged.

This vulnerability is documented in Cisco Bug ID CSCso64762 and has
been assigned Common Vulnerabilities and Exposures (CVE) ID 

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:

Cisco has also provided a CVSS calculator to help compute the
environmental impact for individual networks at:

CSCso64762 - IPS Jumbo frame not processed properly

CVSS Base Score - 7.8
    Access Vector - Network
    Access Complexity - Medium
    Authentication - None
    Confidentiality Impact - Partial
    Integrity Impact - None
    Availability Impact - Complete

CVSS Temporal Score - 6.4
    Exploitability - Functional
    Remediation Level - Official Fix
    Report Confidence - Confirmed


Successful exploitation of the vulnerability may result in a network
denial of service condition. A power cycle is required to recover
operation. An attacker may be able to evade access controls and
detection of malicious activity in the case of Cisco IPS 4260/4270
platforms that have hardware bypass configured to pass traffic in the
event of a kernel panic.

Software Versions and Fixes

When considering software upgrades, also consult 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.

This vulnerability is fixed in Cisco IPS versions 5.1(8)E2 and 6.0(5)
E2 that are expected to be available for download by June 20, 2008.

Fixed software Cisco IPS version 5.1(8)E2 will be available at the
following link:

Fixed software Cisco IPS version 6.0(5)E2 will be available at the
following link:


To workaround this vulnerability, administrators can disable jumbo
Ethernet support on routers and switches directly that are connected
to vulnerable Cisco IPS platforms. This workaround may produce a
negative performance impact in certain environments. Administrators
are encouraged to upgrade to fixed software.

For more information about configuring Jumbo frames on Cisco
switches, please reference the following link:

Obtaining Fixed Software

Cisco has released free software updates that address these
vulnerabilities. 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,
or as otherwise set forth at Downloads at

Do not contact or 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

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:

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
for additional TAC contact information, including localized telephone
numbers, and instructions and e-mail addresses for use in various

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 HD Moore of BreakingPoint

Status of this Notice: FINAL


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.


This advisory is posted on Cisco's worldwide website at:

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:


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-June-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
This includes instructions for press inquiries regarding Cisco security
notices. All Cisco security advisories are available at


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