Cisco Security Advisory: Cisco NX-OS Malformed IP Packet Denial of Service Vulnerability

From: Cisco Systems Product Security Incident Response Team <>
Subject: Cisco Security Advisory: Cisco NX-OS Malformed IP Packet Denial of Service Vulnerability

Hash: SHA256

Cisco Security Advisory: Cisco NX-OS Malformed IP Packet Denial of
Service Vulnerability

Advisory ID: cisco-sa-20120215-nxos

Revision 1.0

For Public Release 2012 February 15 16:00  UTC (GMT)



Cisco NX-OS Software is affected by a denial of service (DoS)
vulnerability that could cause Cisco Nexus 1000v, 5000, and 7000 Series
Switches that are running affected versions of Cisco NX-OS Software to
reload when the IP stack processes a malformed IP packet.

Cisco has released free software updates that address this

This advisory is available at the following link:

Affected Products

Vulnerable Products

Cisco Nexus 1000v, 5000, and 7000 Series Switches that are running
affected versions of Cisco NX-OS Software are affected by this
vulnerability. The vulnerability is in the operating system's IP stack;
therefore, any feature that makes use of the services that are offered
by the IP stack to process IP packets is affected.

Cisco NX-OS Software versions prior to the First Fixed Release version
are affected. Refer to the Software Versions and Fixes section for
details regarding fixed versions.

To determine the version of Cisco NX-OS Software that is running on a
Cisco Nexus switch, administrators can log in to the device and issue
the "show version" command to display the system banner. The following
example shows how to display the version information for the kickstart
and system image that is running on a device that runs Cisco NX-OS
Release 5.1(3):

    switch# show version
    Cisco Nexus Operating System (NX-OS) Software
    TAC support:
    Copyright (c) 2002-2011, Cisco Systems, Inc. All rights reserved.
    The copyrights to certain works contained in this software are
    owned by other third parties and used and distributed under
    license. Certain components of this software are licensed under
    the GNU General Public License (GPL) version 2.0 or the GNU
    Lesser General Public License (LGPL) Version 2.1. A copy of each
    such license is available at and

      BIOS:      version 3.22.0
      kickstart: version 5.1(3)
      system:    version 5.1(3)


Products Confirmed Not Vulnerable

Cisco NX-OS Software for products other than the Cisco Nexus 1000v,
5000, and 7000 Series Switches is not affected by this vulnerability. In
particular, the following products that run Cisco NX-OS Software are not

  * Cisco Nexus 2000 Series Switches
  * Cisco Nexus 3000 Series Switches
  * Cisco Nexus 4000 Series Switches
  * Unified Computing System (UCS)
  * Cisco MDS 9000 Series Multilayer Switches

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


Cisco NX-OS Software is the network operating system used by Cisco
products that are part of the Cisco Data Center switching portfolio,
which includes data center switches such as the Cisco Nexus 5000 Series
and the Cisco Nexus 7000 Series.

Certain versions of Cisco NX-OS Software for Cisco Nexus 1000v, 5000,
and 7000 Series Switches are affected by a vulnerability that may cause
a reload of an affected device when the operating system's IP stack
processes a malformed IP packet and obtaining Layer 4 (UDP or TCP)
information from the packet is required.

The vulnerability is in the operating system's IP stack and any feature
that makes use of services offered by the IP stack to parse IP packets
is affected. For instance, the following scenarios may trigger the
vulnerability because they imply that Layer 4 (UDP or TCP) information
is required to be able to perform the configured function:

  * A malformed, transit IP packet that would normally be forwarded
    by the switch is received and the Time-to-live (TTL) is 1. In
    this case, an ICMP error message (time exceeded) needs to be
    generated. During generation of this ICMP message, the bug could
    be triggered.

  * Policy-based routing is in use, and to make a routing decision,
    an incoming packet needs to be parsed. If the packet is a
    malformed TCP segment and the routing policy uses TCP information
    for routing decisions, then this bug could be triggered.

  * An egress Access Control List (ACL) is applied to an interface
    and a malformed IP packet that needs to be forwarded through that
    interface is received.

Note: This list is not exhaustive. It contains some of the scenarios
that have been confirmed to trigger the vulnerability described in this
document. Other scenarios that require accessing Layer 4 information
of a malformed IP packet may also result in the vulnerability being

Both through-the-device (transit) traffic and to-the-device traffic may
trigger this vulnerability. An affected Cisco Nexus switch that has a
configured IP address is affected by this vulnerability even if the IP
address is used only for management and if the device is configured as a
pure Layer 2 switch; that is, no Layer 3 packet forwarding.

When a system reloads because of this vulnerability, a process called
"netstack" will terminate unexpectedly, and the following message will
be recorded to the system log:

    2012 Feb 02 20:32:15 NX-7010 %SYSMGR-2-SERVICE_CRASHED: Service "netstack" (PID 4335) hasn't caught signal 11 (core will be saved).

This vulnerability is documented in Cisco Bug IDs CSCti23447 and
CSCti49507 (Cisco Nexus 1000v and 7000 Series) and CSCtj01991 (Cisco
Nexus 5000 Series), and has been assigned Common Vulnerabilities and
Exposures (CVE) ID CVE-2012-0352.

Note: Two Cisco Bug IDs are used to track this vulnerability in Cisco
Nexus 1000v and 7000 Series Switches because the vulnerability was
partially fixed by Cisco Bug CSCti23447. The fix was completed with
CSCti49507. For the Cisco Nexus 5000 Series Switches, the vulnerability
was completely fixed by Cisco Bug CSCtj01991

Vulnerability Scoring Details

Cisco has scored the vulnerabilities in this advisory based on the
Common Vulnerability Scoring System (CVSS). The CVSS scoring in this
security advisory is in accordance with CVSS version 2.0.

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

Cisco has provided a base and temporal score. Customers can also
compute environmental scores that help determine the impact of the
vulnerability in their own networks.

Cisco has provided additional information regarding CVSS at the
following link:

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

* CSCti23447, CSCti49507, and CSCtj01991 ("Malformed IP packet causes
Netstack crash")

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 - 6.4
    Exploitability -           Functional
    Remediation Level -        Official-Fix
    Report Confidence -        Confirmed


Successful exploitation of the vulnerability that is described in
this advisory may result in a reload of an affected device. Repeated
exploitation could result in a sustained DoS condition.

Software Versions and Fixes

When considering software upgrades, customers are advised to
consult the Cisco Security Advisories and Responses archive at and review subsequent advisories to
determine exposure and a complete upgrade solution.

In all cases, customers should ensure that the devices to be upgraded
contain sufficient memory and confirm that current hardware and
software configurations will continue to be supported properly by the
new release. If the information is not clear, customers are advised
to contact the Cisco Technical Assistance Center (TAC) or their
contracted maintenance providers.

Each row of the Cisco NX-OS Software table (below) names a Cisco
NX-OS Software 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. A device that
is 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.

|       Platform        |   Major    |  First Fixed Release  |
|                       |  Release   |                       |
| Nexus 1000v Series    | 4.2.x      | 4.2(1)SV1(5.1)        |
| Switches              |            |                       |
|                       | 4.x        | Vulnerable; migrate   |
|                       |            | to 5.x                |
|Nexus 5000 Series      |------------+-----------------------|
| Switches              | 5.0.x      | 5.0(2)N1(1)           |
|                       |------------+-----------------------|
|                       | 5.1.x      | Not vulnerable        |
|                       | 4.2.x      | 4.2.8                 |
|                       |------------+-----------------------|
|                       | 5.0.x      | 5.0.5                 |
|Nexus 7000 Series      |------------+-----------------------|
| Switches              | 5.1.x      | 5.1.1                 |
|                       |------------+-----------------------|
|                       | 5.2.x      | Not vulnerable        |
|                       |------------+-----------------------|
|                       | 6.x        | Not vulnerable        |

Cisco NX-OS Software can be downloaded at


There are no workarounds for the vulnerability described in this

Obtaining Fixed Software

Cisco has released free software updates that address the
vulnerability|vulnerabilities described in this advisory. Prior to
deploying software, customers are advised to consult their
maintenance providers or check the software for feature set
compatibility and known issues that are specific to their

Customers may only install and expect support for feature
sets they have purchased. By installing, downloading,
accessing, or otherwise using such software upgrades, customers
agree to follow the terms of the Cisco software license at,
or as set forth 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, upgrades should be obtained
through the Software Center on at

Customers Using Third-Party Support Organizations

Customers with Cisco products that 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 organization for assistance with the appropriate
course of action.

The effectiveness of any workaround or fix depends on specific
customer situations, such as product mix, network topology, traffic
behavior, and organizational mission. Because of the variety of
affected products and releases, customers should consult their
service providers or support organizations to ensure that any applied
workaround or fix is the most appropriate in the intended network
before it is deployed.

Customers Without Service Contracts

Customers who purchase directly from Cisco but do not hold a Cisco
service contract and customers who make purchases through third-party
vendors but are unsuccessful in obtaining fixed software through
their point of sale should obtain upgrades by contacting the Cisco
Technical Assistance Center (TAC):

  * +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 the product serial number available and be
prepared to provide the URL of this advisory as evidence of
entitlement to a free upgrade. Customers without service contracts
should request free upgrades through the TAC.

Refer to Cisco Worldwide Contacts at
for additional TAC contact information, including localized telephone
numbers, instructions, and e-mail addresses for support in various

Exploitation and Public Announcements

The Cisco Product Security Incident Response Team (PSIRT) is not
aware of any public announcements or malicious use of the
vulnerability that is described in this advisory.

This vulnerability was discovered while working on customer support

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 Security Intelligence Operations at
the following link:

Additionally, a text version of this advisory is clear signed with
the Cisco PSIRT PGP key and circulated among the following e-mail


Future updates of this advisory, if any, will reside on but
may not be announced on mailing lists. Users can monitor this
advisory's URL for any updates.

Revision History

| Revision 1.0 | 2012-February-15  | Initial public release  |

Cisco Security Procedures

Complete information about reporting security vulnerabilities in Cisco
products, obtaining assistance with security incidents, and registering
to receive security information from Cisco is available on at
This web page includes instructions for press inquiries
regarding Cisco Security Advisories. All Cisco Security Advisories are
available at
Version: GnuPG v1.4.11 (GNU/Linux)


Copyright © 1995-2020 All rights reserved.