Summary

• A vulnerability in the Internet Key Exchange Version 2 (IKEv2) module of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause high CPU utilization, traceback messages, or a reload of an affected device that leads to a denial of service (DoS) condition.

  The vulnerability is due to how an affected device processes certain IKEv2 packets. An attacker could exploit this vulnerability by sending specific IKEv2 packets to an affected device to be processed. A successful exploit could allow the attacker to cause high CPU utilization, traceback messages, or a reload of the affected device that leads to a DoS condition.

  Cisco has released software updates that address this vulnerability. There is a workaround that addresses this vulnerability.

  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170927-ike

  This advisory is part of the September 27, 2017, release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication, which includes 12 Cisco Security Advisories that describe 13 vulnerabilities. For a complete list of the advisories and links to them, see Cisco Event Response: September 2017 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco devices that are running a vulnerable release of Cisco IOS Software or Cisco IOS XE Software and have the Internet Security Association and Key Management Protocol (ISAKMP) enabled.

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

  Although only IKEv2 packets can be used to trigger this vulnerability, devices that are running Cisco IOS Software or Cisco IOS XE Software are vulnerable when ISAKMP is enabled.

  A device does not need to be configured with any IKEv2-specific features to be vulnerable.

  Many features use IKEv2, including different types of VPNs such as the following:

  • LAN-to-LAN VPN
  • Remote-access VPN, excluding SSL VPN
  • Dynamic Multipoint VPN (DMVPN)
  • FlexVPN

  The preferred method to determine whether a device has been configured for IKE is to issue the show ip sockets or show udp EXEC command in the CLI. If UDP port 500, UDP port 848, or UDP port 4500 is open on a device, the device is processing IKE packets.

  In the following example, the device is processing IKE packets on UDP port 500 and UDP port 4500, using either IPv4 or IPv6:

  router# show udp 
  
  Proto        Remote      Port      Local       Port  In Out  Stat TTY OutputIF  
  17       --listen--          192.168.130.21    500   0   0 1001011   0   
  17(v6)   --listen--          UNKNOWN           500   0   0 1020011   0   
  17       --listen--          192.168.130.21   4500   0   0 1001011   0   
  17(v6)   --listen--          UNKNOWN          4500   0   0 1020011   0  
  .
  .
  .
  router#

  
  

  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 shows the output of the command for a device that is running Cisco IOS Software Release 15.5(2)T1 and has 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 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 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.

  Cisco has also confirmed that this vulnerability does not affect Cisco ASA 5500 Series Adaptive Security Appliances.

Details

• The IKEv2 protocol is used in the IPsec protocol suite to negotiate cryptographic attributes that will be used to encrypt or authenticate the communication session. These attributes include the cryptographic algorithm, mode, and shared keys. The result of an IKE negotiation is a shared session secret that will be used to derive cryptographic keys.

  Cisco IOS Software and Cisco IOS XE Software support IKEv2 for IPv4 and IPv6 communications. IKEv2 communications can use the following UDP ports:

  • UDP port 500
  • UDP port 848, Group Domain of Interpretation (GDOI)
  • UDP port 4500, Network Address Translation Traversal (NAT-T)

  Only IKEv2 packets can trigger this vulnerability. Although IKEv2 is automatically enabled on Cisco IOS Software and Cisco IOS XE Software when ISAKMP is enabled, the vulnerability can be triggered only by sending IKEv2 packets.

  An attacker could exploit this vulnerability using either IPv4 or IPv6 on any of the listed UDP ports.

Indicators of Compromise

• Depending on the platform and exploit used, impacts of exploitation may differ by platform, including high CPU utilization, traceback messages, or a reload of the affected device that leads to a DoS condition.

  This vulnerability could lead to high CPU utilization by the Crypto IKEv2 process. The following example shows high CPU utilization that may be caused by this vulnerability:

  Router# sh proc cpu sorted
  
  CPU utilization for five seconds: 99%/6%; one minute: 64%; five minutes: 52%
   PID Runtime(ms)     Invoked      uSecs   5Sec   1Min   5Min TTY Process
   PID Runtime(ms)     Invoked      uSecs   5Sec   1Min   5Min TTY Process 
   391     2949388      188131      15677 83.72% 53.79% 43.27%   0 Crypto IKEv2

  Traceback messages triggered by this vulnerability would note CPUHOG indicators for the Crypto IKEv2 process. The following example shows a traceback message that may be caused by this vulnerability:

  date-time: %SYS-3-CPUHOG: Task is running for (2275)msecs, more than (2000)msecs (0/0),process = Crypto IKEv2

  If the device reloads because of this vulnerability, the resulting message would indicate that the Crypto IKEv2 process caused the reload. The following example shows a device reload that results from this vulnerability:

  IOSXE-WATCHDOG: Process = Crypto IKEv2
  

  
  

Workarounds

• If the software release on the device supports the crypto ikev2 limit queue sa-init configuration command (see Cisco bug CSCvc12306), using this command is equivalent to performing an upgrade to a fixed release. Otherwise, there are no workarounds that address this vulnerability.

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:
  https://www.cisco.com/c/en/us/products/end-user-license-agreement.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:
  https://www.cisco.com/c/en/us/support/web/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 3.13.8S-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

• In March 2022, the Cisco Product Security Incident Response Team (PSIRT) became aware of additional attempted exploitation of this vulnerability in the wild. Cisco continues to strongly recommend that customers upgrade to a fixed software release to remediate this vulnerability.

Source

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

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170927-ike

Revision History

• Version	Description	Section	Status	Date
  1.1	Updated exploitation information.	Exploitation and Public Announcements	Final	2022-DEC-16
  1.0	Initial public release.	-	Final	2017-SEP-27

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