Summary

• A vulnerability in the Switch Integrated Security Features of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an interface queue wedge.
  
  The vulnerability is due to incorrect handling of crafted IPv6 packets. An attacker could exploit this vulnerability by sending crafted IPv6 packets through the device. An exploit could allow the attacker to cause an interface queue wedge.
  
  There are no workarounds that address this vulnerability.
  
  This advisory is available at the following link:
  https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180328-sisf

Affected Products

• Vulnerable Products

  This vulnerability affects the Cisco cBR-8 Converged Broadband Router, Cisco ASR 1000 Series Aggregation Services Routers, and Cisco Cloud Services Router 1000V Series when configured with IPv6.

  In the field and internal testing, this vulnerability was only observed or reproduced on the Cisco cBR-8 Converged Broadband Router. The Cisco ASR 1000 Series Aggregation Services Routers and Cisco Cloud Services Router 1000V Series contain the same code logic, so affected trains have had the code fix applied; however, on these two products, the vulnerability has not been observed in the field or successfully reproduced internally.

  For information about which Cisco IOS XE Software releases are vulnerable, consult the Cisco bug ID(s) at the top of this advisory.

  Assessing the IPv6 Configuration

  Administrators can identify interfaces that have assigned IPv6 addresses by using the show ipv6 interface brief command in the CLI. The following example shows the output of the command on a device with IPv6 enabled:

  router#show ipv6 interface brief
  .
  .
  .
  GigabitEthernet0/0/0 [Up/Up]
   fe80::212:daff:fe62:c150
   2001:DB8::1 

  If IPv6 is not supported by the software release that is running on a device, using the show ipv6 interface brief command produces an error message. If IPv6 is not enabled on the device, using the show ipv6 interface brief command does not show any interfaces with IPv6 addresses. In either scenario, the device is not affected by this vulnerability.

  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 Software, Cisco IOS XE Software, or similar text.

  The following example shows the output of the command for a device that is running Cisco IOS XE Software Release 16.2.1 and has an installed image name of CAT3K_CAA-UNIVERSALK9-M:

  ios-xe-device# show version
  
  Cisco IOS Software, Catalyst L3 Switch Software (CAT3K_CAA-UNIVERSALK9-M), Version Denali 16.2.1, RELEASE SOFTWARE (fc1)
  Technical Support: http://www.cisco.com/techsupport
  Copyright (c) 1986-2016 by Cisco Systems, Inc.
  Compiled Sun 27-Mar-16 21:47 by mcpre
  .
  .
  .

  For information about the naming and numbering conventions for Cisco IOS XE Software releases, see the 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 Software, Cisco IOS XR Software, or Cisco NX-OS Software.
  

Indicators of Compromise

• If an interface is queue wedged an admin could observe the input queue via the show interface | include Input queue CLI command. The following example shows the second interface on the router as wedged:
  

  Router#show interface | include Input queue
   Input queue: 0/375/0/0 (size/max/drops/flushes); Total output drops: 0
   Input queue: 376/375/0/0 (size/max/drops/flushes); Total output drops: 0
   Input queue: 0/375/0/0 (size/max/drops/flushes); Total output drops: 0
  Router#

  Once the identified interface is known, capture the output of the show buffers input-interface [interface] packet and show buffers input-interface [interface] dump CLI commands and contact your local support organization.

Workarounds

• There are no workarounds that address this vulnerability. However, it is possible to increase the input queue to a higher value until the source of the issue is identified or the device is upgraded.

Fixed Software

• For detailed information about fixed software releases, consult the Cisco bug ID(s) at the top of this advisory.

  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.

  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.

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.

Source

• This vulnerability was found during the resolution of a Cisco TAC support case.

URL

• https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180328-sisf

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2018-March-28

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