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Cisco Security Advisory

Cisco IOS Software DHCP Denial of Service Vulnerability

Advisory ID: cisco-sa-20120926-dhcp

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20120926-dhcp

Revision 1.0

For Public Release 2012 September 26 16:00  UTC (GMT)


Summary

Cisco IOS Software contains a vulnerability that could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition. An attacker could exploit this vulnerability by sending a single DHCP packet to or through an affected device, causing the device to reload.

Cisco has released free software updates that address this vulnerability. A workaround that mitigates this vulnerability is available. This advisory is available at the following link:
http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20120926-dhcp

Note: The September 26, 2012, Cisco IOS Software Security Advisory bundled publication includes nine Cisco Security Advisories. Eight of the advisories address vulnerabilities in Cisco IOS Software, and one advisory addresses a vulnerability in Cisco Unified Communications Manager. Each Cisco IOS Software Security Advisory lists the Cisco IOS Software releases that correct the vulnerability or vulnerabilities detailed in the advisory as well as the Cisco IOS Software releases that correct all Cisco IOS Software vulnerabilities in the September 2012 bundled publication. 

Individual publication links are in "Cisco Event Response: Semi-Annual Cisco IOS Software Security Advisory Bundled Publication" at the following link:

http://www.cisco.com/web/about/security/intelligence/Cisco_ERP_sep12.html


Affected Products


Vulnerable Products

Cisco devices that are running Cisco IOS Software versions that include the Device Sensor feature are affected by this vulnerability. Devices that have at least one interface with an IP address are affected.

To determine whether the Cisco IOS Software release includes the Device Sensor feature, issue the show subsys command.  

The following example shows the Device Sensor feature is included:
Switch#show subsys | include dsensor_lite
dsensor_lite                       Protocol    1.000.001
To determine whether an interface is assigned an IP address, issue the show ip interface brief command.  

The following example indicates the FastEthernet1/0 interface is assigned IP address 10.10.10.1:
router#show ip interface brief 
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet1/0            10.10.10.1      YES manual up                    up      
FastEthernet1/1            unassigned      YES NVRAM  up                    up

To determine the Cisco IOS 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 Software by displaying text similar to "Cisco Internetwork Operating System Software" or "Cisco IOS Software." The image name displays in parentheses, followed by "Version" and the Cisco IOS Software release name. Other Cisco devices do not have the show version command or may provide different output.

The following example identifies a Cisco product that is running Cisco IOS Software Release 15.0(1)M1 with an installed image name of C3900-UNIVERSALK9-M:

Router> show version 
Cisco IOS Software, C3900 Software (C3900-UNIVERSALK9-M), Version 15.0(1)M1, RELEASE SOFTWARE (fc1)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2009 by Cisco Systems, Inc.
Compiled Wed 02-Dec-09 17:17 by prod_rel_team
!--- output truncated 

Additional information about Cisco IOS Software release naming conventions is available in "White Paper: Cisco IOS and NX-OS Software Reference Guide" at http://www.cisco.com/web/about/security/intelligence/ios-ref.html.



Products Confirmed Not Vulnerable

Cisco IOS XE and Cisco IOS XR Software are not affected by this vulnerability.

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

Details

The Device Sensor feature of Cisco IOS Software is used to gather raw endpoint data from network devices that are using protocols such as Cisco Discovery Protocol, Link Layer Discovery Protocol (LLDP), and DHCP. The endpoint data is available to registered clients in the context of an access session.

Cisco IOS Software contains a vulnerability that could allow an unauthenticated, remote attacker to cause a DoS condition. An attacker could exploit this vulnerability by sending a single DHCP packet to or through an affected device, causing the device to reload.

The Device Sensor feature, enabled by default, is vulnerable on devices that have at least one interface with an IP address. The vulnerability is triggered when the Device Sensor feature attempts to process a DHCP packet. In affected releases, valid DHCP packets could trigger this vulnerability. 

For more information about the Device Sensor feature, please refer to the Device Sensor Guide.

This vulnerability was previously documented in Cisco bug ID CSCty96049 (registered customers only) and has been assigned the Common Vulnerabilities and Exposures (CVE) ID CVE-2012-4621.

Vulnerability Scoring Details

Cisco has scored the vulnerability 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:

http://www.cisco.com/web/about/security/intelligence/cvss-qandas.html

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

http://intellishield.cisco.com/security/alertmanager/cvss

CSCty96049 - Cisco IOS Software DHCP Server Denial of Service Vulnerability

Calculate the environmental score of CSCty96049

CVSS Base Score - 7.8

Access Vector

Access Complexity

Authentication

Confidentiality Impact

Integrity Impact

Availability Impact

Network

Low

None

None

None

Complete

CVSS Temporal Score - 6.4

Exploitability

Remediation Level

Report Confidence

Functional

Official-Fix

Confirmed


Impact

Successful exploitation of the vulnerability may cause an affected device to reload.  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 http://www.cisco.com/go/psirt 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.

Cisco IOS Software

Each row of the following Cisco IOS Software table corresponds to a Cisco IOS Software train. If a particular train is vulnerable, the earliest releases that contain the fix are listed in the First Fixed Release column. The First Fixed Release for All Advisories in the September 2012 Bundled Publication column lists the earliest possible releases that correct all the published vulnerabilities in the Cisco IOS Software Security Advisory bundled publication. Cisco recommends upgrading to the latest available release, where possible.

The Cisco IOS Software Checker allows customers to search for Cisco Security Advisories that address specific Cisco IOS Software releases. This tool is available on the Cisco Security Intelligence Operations (SIO) portal at http://tools.cisco.com/security/center/selectIOSVersion.x

Major Release      Availability of Repaired Releases
Affected 12.0-Based Releases First Fixed Release First Fixed Release for All Advisories in the September 2012 Cisco IOS Software Security Advisory Bundled Publication
There are no affected 12.0 based releases
Affected 12.2-Based Releases First Fixed Release First Fixed Release for All Advisories in the September 2012 Cisco IOS Software Security Advisory Bundled Publication
There are no affected 12.2 based releases
Affected 12.3-Based Releases First Fixed Release First Fixed Release for All Advisories in the September 2012 Cisco IOS Software Security Advisory Bundled Publication
There are no affected 12.3 based releases
Affected 12.4-Based Releases First Fixed Release First Fixed Release for All Advisories in the September 2012 Cisco IOS Software Security Advisory Bundled Publication
There are no affected 12.4 based releases
Affected 15.0-Based Releases First Fixed Release First Fixed Release for All Advisories in the September 2012 Cisco IOS Software Security Advisory Bundled Publication
15.0EX Not vulnerable
Not vulnerable
15.0EY Not vulnerable
Not vulnerable
15.0M Not vulnerable
15.0(1)M9
15.0MR Not vulnerable
Vulnerable; contact your support organization per the instructions in Obtaining Fixed Software section of this advisory.
15.0MRA Not vulnerable
Vulnerable; contact your support organization per the instructions in Obtaining Fixed Software section of this advisory.
15.0S Not vulnerable

Cisco IOS XE devices: Please see Cisco IOS XE Software Availability
15.0(1)S6

Cisco IOS XE devices: Please see Cisco IOS XE Software Availability
15.0SE 15.0(1)SE3
15.0(2)SE
15.0(2)SE1; Available on 10-DEC-12

15.0(2)SE
15.0SG Not vulnerable

Cisco IOS XE devices: Please see Cisco IOS XE Software Availability
15.0(2)SG5
15.0(2)SG6 ; Available on 11-OCT-12

Cisco IOS XE devices: Please see Cisco IOS XE Software Availability
15.0SY Not vulnerable
15.0(1)SY2
15.0XA Not vulnerable
Vulnerable; First fixed in Release 15.1M
15.0XO Cisco IOS XE devices: Please see Cisco IOS-XE Software Availability

Cisco IOS XE devices: Please see Cisco IOS-XE Software Availability
Affected 15.1-Based Releases First Fixed Release First Fixed Release for All Advisories in the September 2012 Cisco IOS Software Security Advisory Bundled Publication
15.1EY Not vulnerable
15.1(2)EY4
15.1GC Not vulnerable
Vulnerable; First fixed in Release 15.1M
15.1M Not vulnerable
15.1(4)M5
15.1MR Not vulnerable
15.1(3)MR; Available on 01-OCT-12
15.1S Not vulnerable

Cisco IOS XE devices: Please see Cisco IOS XE Software Availability

15.1(3)S
Cisco IOS XE devices: Please see Cisco IOS XE Software Availability
15.1SG 15.1(1)SG1
15.1(2)SG; Available on 12-NOV-12

Cisco IOS XE devices: Please see Cisco IOS XE Software Availability
15.1(1)SG1

15.1(2)SG 12-NOV-12
Cisco IOS XE devices: Please see Cisco IOS XE Software Availability
15.1SNG Not vulnerable
Vulnerable; contact your support organization per the instructions in Obtaining Fixed Software section of this advisory.
15.1SNH Not vulnerable
Vulnerable; contact your support organization per the instructions in Obtaining Fixed Software section of this advisory.
15.1SNI Not vulnerable
Vulnerable; migrate to any release in 15.2SNG
15.1SV Vulnerable; contact your support organization per the instructions in Obtaining Fixed Software section of this advisory.
Vulnerable; contact your support organization per the instructions in Obtaining Fixed Software section of this advisory.
15.1T Not vulnerable
Vulnerable; First fixed in Release 15.1M
15.1XB Not vulnerable
Vulnerable; First fixed in Release 15.1M
Affected 15.2-Based Releases First Fixed Release First Fixed Release for All Advisories in the September 2012 Cisco IOS Software Security Advisory Bundled Publication
15.2GC Not vulnerable
Releases prior to 15.2(3)GC are vulnerable; Releases 15.2(3)GC and later are not vulnerable. First fixed in Release 15.2T
15.2JA Not vulnerable
Not Vulnerable
15.2M Not vulnerable

Not vulnerable
15.2S 15.2(2)S1

Cisco IOS XE devices: Please see Cisco IOS XE Software Availability
15.2(1)S2
15.2(2)S1
15.2(4)S

Cisco IOS XE devices: Please see Cisco IOS XE Software Availability
15.2SNG Not vulnerable
Not vulnerable
15.2T Not vulnerable
15.2(1)T3
15.2(2)T2
15.2(3)T2; Available on 12-OCT-12


Cisco IOS XE Software

Cisco IOS XE Software is not affected by this vulnerability.

Cisco IOS XR Software

Cisco IOS XR Software is not affected by this vulnerability.


Workarounds

In affected releases, the Device Sensor feature is enabled by default. It is possible to mitigate the vulnerability in this advisory by applying the global configuration command device-sensor filter-spec dhcp exclude all. This command will filter the Device Sensor feature collection of DHCP packets, and the Device Sensor feature will no longer process or store DHCP information.  

In the following example, the global configuration command is issued:

Switch# configure terminal
Switch(config)# device-sensor filter-spec dhcp exclude all

To confirm that the Device Sensor feature is no longer collecting DHCP data, issue the show device-sensor cache all command. No DHCP entries should be present in the table.  

In the following example, the following table contains only Cisco Discover Protocol data:

Switch# show device-sensor cache all
Device: 000f.f7a7.234f on port GigabitEthernet2/1
--------------------------------------------------
Proto Type:Name Len Value
cdp 22:mgmt-address-type 8 00 16 00 08 00 00 00 00
cdp 19:cos-type 5 00 13 00 05 00
cdp 18:trust-type 5 00 12 00 05 00
cdp 11:duplex-type 5 00 0B 00 05 01
cdp 10:native-vlan-type 6 00 0A 00 06 00 01
cdp 9:vtp-mgmt-domain-type 9 00 09 00 09 63 69 73 63 6F

Obtaining Fixed Software

Cisco has released free software updates that address the vulnerability 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 environments.

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 http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html.

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 Navigator on Cisco.com at http://www.cisco.com/cisco/software/navigator.html.

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: tac@cisco.com

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 http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html for additional TAC contact information, including localized telephone numbers, instructions, and e-mail addresses for support in various languages.

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 found during the troubleshooting of customer service requests.

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 Security Intelligence Operations at the following link:

http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20120926-dhcp

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

  • cust-security-announce@cisco.com
  • first-bulletins@lists.first.org
  • bugtraq@securityfocus.com
  • vulnwatch@vulnwatch.org
  • cisco@spot.colorado.edu
  • cisco-nsp@puck.nether.net
  • full-disclosure@lists.grok.org.uk

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


Revision History

Revision 1.0 2012-September-26 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 Cisco.com at http://www.cisco.com/web/about/security/psirt/security_vulnerability_policy.html. This web page includes instructions for press inquiries regarding Cisco Security Advisories. All Cisco Security Advisories are available at http://www.cisco.com/go/psirt.
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