Cisco IOS Software DHCP Denial of Service Vulnerability

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 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.
  
  

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

Fixed Software

• 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 (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.
  
  

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.

URL

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

Revision History

• Revision 1.0

  2012-September-26

  Initial public release.

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