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HistoryMay 26, 2011 - 12:00 a.m.

Cisco Security Advisory: Cisco IOS XR Software IP Packet Vulnerability






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Cisco Security Advisory: Cisco IOS XR Software IP Packet

Advisory ID: cisco-sa-20110525-iosxr

Revision 1.0

For Public Release 2011 May 25 1600 UTC (GMT)



Cisco IOS XR Software Releases 3.8.3, 3.8.4, and 3.9.1 are affected
by a vulnerability that an unauthenticated, remote user can trigger
by sending specific IP version 4 (IPv4) packets to or through an
affected device.

Successful exploitation could cause the NetIO process to restart.
Under a sustained attack, the Cisco CRS Modular Services Card (MSC)
on a Cisco Carrier Routing System (CRS) or a Line Card on a Cisco
12000 Series Router or Cisco ASR 9000 Series Aggregation Services
Router will reload.

Cisco has released free Software Maintenance Units (SMU) that address
this vulnerability.

There are no workarounds for this vulnerability.

This advisory is posted at:

Affected Products

This vulnerability affects any device that is running Cisco IOS XR
Software Releases 3.8.3, 3.8.4, or 3.9.1 and has an IPv4 address
configured on one of the interfaces of a Cisco Line Card or Cisco CRS

Vulnerable Products

Cisco IOS XR Software Releases 3.8.3, 3.8.4, and 3.9.1 are affected
when they are running on the following Cisco hardware platforms:

  • Cisco ASR 9000 Series Aggregation Services Routers
  • Cisco Carrier Routing System
  • Cisco XR 12000 Series Routers

To determine the Cisco IOS XR Software release that is running on a
Cisco product, administrators can log in to the device and issue the
show version command to display the system banner. The system banner
confirms that the device is running Cisco IOS XR Software by
displaying text similar to "Cisco IOS XR Software". The software
version is displayed after the text "Cisco IOS XR Software".

The following example identifies a Cisco XR 12000 Series Router that
is running Cisco IOS XR Software Release 3.9.1:

RP/0/0/CPU0:example#show version
Wed Dec 15 10:16:47.117 singa

Cisco IOS XR Software, Version 3.9.1[00]
Copyright (c) 2010 by Cisco Systems, Inc.

ROM: System Bootstrap, Version 12.0(20090302:133850) [rtauro-sw30346-33S 1.23dev(0.36)]

Copyright (c) 1994-2009 by cisco Systems, Inc.

example uptime is 26 minutes
System image file is "disk0:c12k-os-mbi-3.9.1/mbiprp-rp.vm"

cisco 12404/PRP (7457) processor with 3145728K bytes of memory.
7457 processor at 1266Mhz, Revision 1.2

1 Cisco 12000 Series Performance Route Processor
1 Cisco 12000 Series SPA Interface Processor-601/501/401
1 Cisco 12000 4 Port Gigabit Ethernet Controller (4 GigabitEthernet)
3 Management Ethernet
8 FastEthernet
4 GigabitEthernet/IEEE 802.3 interface(s)
1019k bytes of non-volatile configuration memory.
982304k bytes of disk0: (Sector size 512 bytes).
62420k bytes of disk1: (Sector size 512 bytes).
65536k bytes of Flash internal SIMM (Sector size 256k).

!--- output truncated

Products Confirmed Not Vulnerable

No other releases of Cisco IOS XR Software are affected.

The following products are not affected by this vulnerability:

  • Cisco IOS Software
  • Cisco IOS XE Software for Cisco ASR 1000 Series Routers
  • Cisco NX-OS Software

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


Cisco IOS XR Software, which is part of the Cisco IOS Software
family, uses a microkernel-based distributed operating system
infrastructure. Cisco IOS XR Software runs on the Cisco CRS, Cisco
12000 Series Routers, and Cisco ASR 9000 Series Aggregation Services

More information on Cisco IOS XR Software is available at the
following link:

This vulnerability affects any device that is running affected
releases of Cisco IOS XR Software and has an IPv4 address configured
on one of the interfaces of a Cisco Line Card or Cisco CRS MSC.

When a Cisco Line Card or Cisco CRS MSC sends a specific IPv4 packet,
the NetIO process will restart. If the NetIO process is restarted
several times, the Cisco Line Card or Cisco CRS MSC will reload,
which could cause a denial of service (DoS) condition for traffic
that is transiting the affected line cards.

Although a crash is caused by a packet that originates from the Cisco
Line Card or Cisco CRS MSC, an unauthenticated, remote user can
trigger the vulnerability by sending specific IP packets to or
through the device. In the latter scenario, the Cisco Line Card or
Cisco CRS MSC will create the specific IPv4 packet response that
triggers the vulnerability

This vulnerability is documented in Cisco bug ID CSCth44147 (
registered customers only) and has been assigned CVE ID

Vulnerability Scoring Details

Cisco has provided scores for the vulnerability 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

  • CSCth44147: NetIO Process crashes when generating specific IP packet

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 may result in a reload
of the Cisco CRS MSC on a Cisco CRS or the line cards on a Cisco
12000 Series Router or Cisco ASR 9000 Series Aggregation Services
Router. Repeated exploitation could result in a sustained DoS

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.

| Major | Availability of Repaired Releases | |
| Release | | |
| Affected | | | | |
| 3.2.X | | | First | |
| through | SMU ID | SMU NAME | Fixed | |
| 3.7.X - | | | Release | |
| Based | | | | |
| Releases | | | | |
| There are no affected 3.2.X through 3.7.X - based releases | |
| Affected | | | First | |
| 3.8.X | SMU ID | SMU NAME | Fixed | |
| Based | | | Release | |
| Releases | | | | |
| 3.8.0 | Not Vulnerable. |
| 3.8.1 | Not Vulnerable. |
| 3.8.2 | Not Vulnerable. |
| | CRS: | | No first | |
| | AA04566 | hfr-base-3.8.3.CSCth44147 | fixed | |
| | | | release; | |
| |----------±----------------------------|migrate |–|
| 3.8.3 | ASR9K | Not Applicable | to | |
| | | | 3.9.X, | |
| |----------±----------------------------|4.0.X, |–|
| | XR12000 | Not Applicable | or | |
| | | | later. | |
| | CRS: | | No first | |
| | AA04565 | hfr-base-3.8.4.CSCth44147 | fixed | |
| | | | release; | |
| |----------±----------------------------|migrate |–|
| 3.8.4 | ASR9K | Not Applicable | to | |
| | | | 3.9.2, | |
| |----------±----------------------------|4.X.0, |–|
| | XR12000: | | or | |
| | AA04567 | c12k-base-3.8.4.CSCth44147 | later. | |
| | | | | |
| Affected | | | First | |
| 3.9.X | SMU ID | SMU NAME | Fixed | |
| Based | | | Release | |
| Releases | | | | |
| 3.9.0 | Not Vulnerable. |
| | CRS: | hfr-base-3.9.1.CSCth44147 | | |
| | AA04564 | | | |
| |----------±----------------------------| |–|
| 3.9.1 | ASR9K: | asr9k-base-3.9.1.CSCth44147 | 3.9.2 | |
| | AA04563 | | | |
| |----------±----------------------------| |–|
| | XR12000: | c12k-base-3.9.1.CSCth44147 | | |
| | AA04530 | | | |
| 3.9.2 | Not Vulnerable. |
| Affected | | |
| 4.0.X - | There are no affected 4.0.X - based releases | |
| based | | |
| Releases. | | |
| Affected | | |
| 4.1.X | There are no affected 4.1.X based releases. | |
| Based | | |
| Releases | | |


There are no workarounds for this vulnerability.

Using Infrastructure Access Control Lists (iACLs) may help limit the
attack surface of this vulnerability. Although it is often difficult
to block traffic that transits a network, it is possible to identify
traffic that should never be allowed to target infrastructure devices
and block that traffic at the border of networks. iACLs are a network
security best practice and should be considered as a long-term
addition to good network security. Because some packets that may be
used to exploit this vulnerability could utilize UDP as a transport,
an attacker could spoof the sender's IP address, which may defeat
ACLs that permit communication to these ports from trusted IP
addresses. To provide a better mitigation solution, administrators
should consider using Unicast Reverse Path Forwarding (Unicast RPF)
in conjunction with iACLs.

For more information on iACLs, consult the document "Limit Network
Access with Access Control Lists" at 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 [email protected] or [email protected] 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: [email protected]

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 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 the handling of customer
support calls.

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 | 2011-May-25 | 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

Copyright 2010-2011 Cisco Systems, Inc. All rights reserved.
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