Summary

• A vulnerability in the Internet Key Exchange Version 2 (IKEv2) implementation in Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to prevent IKEv2 from establishing new security associations.

  The vulnerability is due to incorrect handling of crafted IKEv2 SA-Init packets. An attacker could exploit this vulnerability by sending crafted IKEv2 SA-Init packets to the affected device. An exploit could allow the attacker to cause the affected device to reach the maximum incoming negotiation limits and prevent further IKEv2 security associations from being formed.

  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-ikev2-9p23Jj2a

  This advisory is part of the June 3, 2020, release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication, which includes 23 Cisco Security Advisories that describe 25 vulnerabilities. For a complete list of the advisories and links to them, see Cisco Event Response: June 2020 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 or IOS XE Software and have IKEv2 features configured.

  Devices configured with only IKEv1 features are not affected.

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

  Many features can 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
  • Group Encrypted Transport VPN (GET VPN)

  Assessing Whether IKEv2 Is Enabled

  1. Assess whether the device is configured with IKE (version 1 or 2)

  Administrators can use the show ip sockets or show udp EXEC command in the CLI to see if IKE processing is enabled (this will show for both IKEv1 and IKEv2 as both use the same port numbers). If UDP port 500, UDP port 848, UDP port 4500, or UDP port 4848 is open on a device, the device is processing IKE packets.

  The following example shows the output of the show udp command on a device that is processing IKE packets on UDP port 500 and UDP port 4500, using either IP Version 4 (IPv4) or IP Version 6 (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#
  

  If the command returns no output, or the command returns an error, then the device is not vulnerable. If the device returns output for any of the above mentioned UDP ports for IKE then proceed to the next step.

  2. Assess whether the device's IKE configuration is using IKEv2

  If the show udp command shows that the device is listening for IKE traffic, an administrator can assess if the device is configured to use IKEv2 by entering the CLI command show running-config | include ikev2|gikev2. If the command returns output, the configuration is most likely set up to process IKEv2 or G-IKEv2 traffic and is therefore affected.  

  Note: Some customers may have entered IKEv2 commands but never associated them with appropriate features. Reviewing the full configuration or examining the output of the various show crypto ikev2 CLI commands can help determine if IKEv2 is properly configured.

  Products Confirmed Not Vulnerable

  Only products listed in the Vulnerable Products section of this advisory are 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

• Cisco IOS and 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)
  • UDP port 4848, GDOI NAT-T 

  An attacker could exploit this vulnerability by using IPv4 or IPv6 on any of the UDP ports in the preceding list. Traffic needs to be targeted at the affected device.

Workarounds

• There are no workarounds that address this vulnerability.

  If the device has hit the max-in-negotiation-sa limits and they are not clearing automatically, there is no way to clear the in-negotiation queue. The only way to recover the device is to power-cycle it. If the source of the attack has been identified and stopped, an administrator can increase the size of the max-in-negotiation-sa queue to allow the device to function until a power cycle can be scheduled by increasing the configured max-in-negotiation-sa queue as shown in the following example:

  Router#configure terminal
  Router(config)#crypto ikev2 limit max-in-negotiation-sa 300
  Router(config)#end
  Router#
  

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 the Cisco Software Checker to identify 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 the Cisco Software Checker to search advisories in the following ways:

  • Choose the software and one or more releases
  • Upload a .txt file that includes a list of specific releases
  • Enter the output of the show version command

  After initiating a search, customers can customize the search to include all Cisco Security Advisories, a specific advisory, or all advisories in the most recent bundled publication.

  Customers can also use the following form to determine whether a release is affected by any Cisco Security Advisory by entering a Cisco IOS or IOS XE Software release—for example, 15.1(4)M2 or 3.13.8S:

  By default, the Cisco Software Checker includes results only for vulnerabilities that have a Critical or High Security Impact Rating (SIR). To include results for Medium SIR vulnerabilities, customers can use the Cisco Software Checker on Cisco.com and check the Medium check box in the drop-down list under Impact Rating when customizing a search.

  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 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://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ikev2-9p23Jj2a

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2020-JUN-03

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