Summary

• A vulnerability in the Autonomic Networking Infrastructure (ANI) registrar feature of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition.
  
  The vulnerability is due to incomplete input validation on certain crafted packets. An attacker could exploit this vulnerability by sending a crafted autonomic network channel discovery packet to a device that has all the following characteristics:
  

  • Running a Cisco IOS Software or Cisco IOS XE Software release that supports the ANI feature
  • Configured as an autonomic registrar
  • Has a whitelist configured

  
  An exploit could allow the attacker to cause the affected device to reload.
  
  Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.
  
  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170320-ani
  
  Note: Also see the companion advisory for affected devices that support Autonomic Networking: Cisco IOS and IOS XE Software IPv6 Denial of Service Vulnerability.

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco IOS Software and Cisco IOS XE Software devices with all the following characteristics:

  • Running a release of Cisco IOS Software or Cisco IOS XE Software that supports the ANI feature
  • Configured as an autonomic registrar
  • Has a configured whitelist

  Note: Autonomic networking should be configured with a whitelist. Do not remove the whitelist as a workaround.

  For information about which Cisco IOS and IOS XE Software releases are vulnerable, see the Fixed Software section of this advisory.

  Determining Whether a Device is Configured as an Autonomic Network Registrar

  Administrators can identify a device that is configured as an autonomic registrar by using the show autonomic device command in the CLI. The following example shows the output of the command on a device that is configured as an autonomic registrar:

  Device# show autonomic device 
                                                                                  
  	Status                         Enabled
  	Type                                                    Autonomic Registrar
  	UDI                            PID:ASR1002-X SN:FOX2005GAHG
  	Device ID                      cc16.7ec4.2d00-1
  	Domain ID                      cisco.com
  	Domain Certificate             (sub:) ou=cisco.com+serialNumber=PID:ASR1002-X SN:FOX2005GAHG,cn=cc16.7ec4.2d00-1
  	Certificate Serial Number      02
  	Device Address                 FD08:2EEF:C2EE:0:CC16:7EC4:2D00:1
  	Domain Cert is Valid     
                                                                                  
  Device#

  A device that is not configured as an autonomic registrar will indicate a Type of Autonomic Node or return different output.

  Administrators can determine whether an autonomic registrar is configured with a whitelist by using the show autonomic registrar command in the CLI. The registrar must have a whitelist configured to be vulnerable. If the whitelist is configured, the output shows the location of the whitelist file. A device configured as an autonomic registrar without a whitelist configuration will have a blank field next to the Whitelist output:

  Device# show autonomic registrar
  
          Domain Name                   cisco
          Whitelist                                             bootflash:whitelist.txt
          Status                        ANR Live
          Address                       FD7A:F78C:911D::D253:5185:5472
          Certificate (sub:)            cn=ANRA-CS
  

  Determining the Cisco IOS Software Release

  To determine which Cisco IOS Software release is running on a device, administrators can log in to the device, use the show version command in the CLI, and then refer to the system banner that appears. If the device is running Cisco IOS Software, the system banner displays text similar to Cisco Internetwork Operating System Software or Cisco IOS Software. The banner also displays the installed image name in parentheses, followed by the Cisco IOS Software release number and release name. Some Cisco devices do not support the show version command or may provide different output.

  The following example identifies a Cisco product that is running Cisco IOS Software Release 15.5(2)T1 with an installed image name of C2951-UNIVERSALK9-M:

  Router> show version
  
  Cisco IOS Software, C2951 Software (C2951-UNIVERSALK9-M), Version 15.5(2)T1, RELEASE SOFTWARE (fc1)
  Technical Support: http://www.cisco.com/techsupport
  Copyright (c) 1986-2015 by Cisco Systems, Inc.
  Compiled Mon 22-Jun-15 09:32 by prod_rel_team
  .
  .
  .

  For information about the naming and numbering conventions for Cisco IOS Software releases, see White Paper: Cisco IOS and NX-OS Software Reference Guide.

  Determining the Cisco IOS XE Software Release

  To determine which Cisco IOS XE Software release is running on a device, administrators can log in to the device, use the show version command in the CLI, and then refer to the system banner that appears. If the device is running Cisco IOS XE Software, the system banner displays Cisco IOS XE Software or similar text.

  The following example shows the output of the show version command on a device that is running Cisco IOS XE Software Release 3.16.1aS:

  Router> show version
  
  Cisco IOS XE Software, Version 03.16.01a.S - Extended Support Release
  Cisco IOS Software, ASR1000 Software (PPC_LINUX_IOSD-ADVENTERPRISEK9-M), Version 15.5(3)S1a, RELEASE SOFTWARE (fc1)
  Technical Support: http://www.cisco.com/techsupport
  Copyright (c) 1986-2015 by Cisco Systems, Inc.
  Compiled Wed 04-Nov-15 17:40 by mcpre
  .
  .
  .

  For information about the naming and numbering conventions for Cisco IOS XE Software releases, see White Paper: Cisco IOS and NX-OS Software Reference Guide.

  Products Confirmed Not Vulnerable

  No other Cisco products are currently known to be affected by this vulnerability.
  
  Cisco has confirmed that this vulnerability does not affect Cisco IOS XR Software or Cisco NX-OS Software.

Details

• The frames that exploit this vulnerability are Layer 2 adjacent. An ANI proxy will forward the packets to the registrar. As a result, a new client that is multiple hops from the registrar could achieve this exploit. Therefore, the Cisco Product Security Incident Response Team (PSIRT) has published this vulnerability with a High Security Impact Rating.

Indicators of Compromise

• Exploitation of this vulnerability will cause an affected device to reload. Exploitation may be confirmed by decoding the stack trace for the device and determining whether the AN HELPER process crashed. If the process crashed, device logs will contain an error message similar to the following example:
  

  %LINK-3-UPDOWN: Interface ANI2, changed state to up
  %LINEPROTO-5-UPDOWN: Line protocol on Interface ANI2, changed state to up
  
  Exception to IOS Thread:
  Frame pointer 0x7F5EB1B173D0, PC = 0x557F33057009
  
  UNIX-EXT-SIGNAL: Segmentation fault(11), Process = AN HELPER
  .
  .
  .

Workarounds

• There are no workarounds that address this vulnerability. Autonomic networking should be configured with a whitelist. Do not remove the whitelist as a workaround.

Fixed Software

• Cisco has released free software updates that address the vulnerability described in this advisory. Customers may only install and expect support for software versions and feature sets for which they have purchased a license. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco software license:
  http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html

  Additionally, customers may only download software for which they have a valid license, procured from Cisco directly, or through a Cisco authorized reseller or partner. In most cases this will be a maintenance upgrade to software that was previously purchased. Free security software updates do not entitle customers to a new software license, additional software feature sets, or major revision upgrades.

  When considering software upgrades, customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories and Alerts page, 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.

  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 TAC:
  http://www.cisco.com/en/US/support/tsd_cisco_worldwide_contacts.html

  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.

  Cisco IOS and IOS XE Software

  To help customers determine their exposure to vulnerabilities in Cisco IOS and IOS XE Software, Cisco provides a tool, the Cisco IOS Software Checker, that identifies any Cisco Security Advisories that impact a specific software release and the earliest release that fixes the vulnerabilities described in each advisory (“First Fixed”). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities described in all the advisories identified (“Combined First Fixed”).

  Customers can use this tool to perform the following tasks:

  • Initiate a search by choosing one or more releases from a drop-down menu or uploading a file from a local system for the tool to parse
  • Enter the output of the show version command for the tool to parse
  • Create a custom search by including all previously published Cisco Security Advisories, a specific advisory, or all advisories in the most recent bundled publication

  To determine whether a release is affected by any published Cisco Security Advisory, use the Cisco IOS Software Checker on Cisco.com or enter a Cisco IOS Software or Cisco IOS XE Software release—for example, 15.1(4)M2 or 3.1.4S—in the following field:

  For a mapping of Cisco IOS XE Software releases to Cisco IOS Software releases, refer to the Cisco IOS XE 2 Release Notes, Cisco IOS XE 3S Release Notes, or Cisco IOS XE 3SG Release Notes, depending on the Cisco IOS XE Software release.

Exploitation and Public Announcements

• The Cisco Product Security Incident Response Team (PSIRT) is not aware of malicious use of the vulnerability that is described in this advisory. Omar Eissa of ERNW disclosed this vulnerability at the TROOPERS17 conference in Germany in March 2017.

Source

• This vulnerability was reported to Cisco by Omar Eissa of ERNW.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170320-ani

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2017-March-20

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