Summary

• A vulnerability in Simple Network Management Protocol (SNMP) functions of Cisco ASR 1000 Series Aggregation Services Routers running Cisco IOS XE Software Release 3.13.6S, 3.16.2S, or 3.17.1S could allow an authenticated, remote attacker to cause high CPU usage on an affected device, resulting in a denial of service (DoS) condition.
  
  The vulnerability is due to an incorrect initialized variable. An attacker could exploit this vulnerability by performing SNMP polling on MIBs and using only Interface Index (ifIndex) values. A successful exploit could allow the attacker to increase CPU usage to 99% on an affected device and cause a DoS condition.
  
  There are workarounds that address this vulnerability.
  
  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170201-asrsnmp

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco ASR 1000 Series Aggregation Services Routers that are running Cisco IOS XE Software Release 3.13.6S, 3.16.2S, or 3.17.1S.

  
  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 3.17.01.S:
  
  

  Router> show version
  
  Cisco IOS XE Software, Version 03.17.01.S - Standard Support Release
  Cisco IOS Software, ASR903 Software (PPC_LINUX_IOSD-UNIVERSALK9_NPE-M), Version 15.6(1)S1, RELEASE SOFTWARE (fc3)
  Technical Support: http://www.cisco.com/techsupport
  Copyright (c) 1986-2016 by Cisco Systems, Inc.
  Compiled Wed 09-Mar-16 06:34 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.

Indicators of Compromise

• Exploitation of this vulnerability will cause high CPU usage by the SNMP engine on an affected device. To assess CPU usage on a device, administrators can use the show process cpu sorted command in the CLI. The following example shows the output of the command for a device that has high CPU usage by the SNMP engine, indicated in bold:
  

  STLD1-630-03.03-ASR1000-RU38# show process cpu sorted
  CPU utilization for five seconds: 100%/0%; one minute: 100%; five minutes: 100%
   PID Runtime(ms)     Invoked      uSecs   5Sec   1Min   5Min TTY Process 
   54   1600083478    33340088	  47993	99.97% 99.94% 99.95%   0 SNMP ENGINE
  .
  .
  .

  Exploitation of this vulnerability may also cause a %SNMP-3-INPUT_QFULL_ERR: Packet dropped due to input queue full error to occur.

Workarounds

• If the device console is accessible, administrators can remove the SNMP configuration to allow the CPU to recover and allow for a device upgrade to a fixed release of the software.
  
  If the device console is not accessible, administrators can power cycle the device and either remove the SNMP configuration or prevent SNMP polling on the device to allow for a device upgrade to a fixed release of the software.

Fixed Software

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

  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 discovered while responding to customer support requests.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170201-asrsnmp

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2017-February-01

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