Summary

• A vulnerability in the IPSec decryption routine of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload, resulting in a denial of service (DoS) condition. 

  This vulnerability is due to buffer exhaustion that occurs while traffic on a configured IPsec tunnel is being processed. An attacker could exploit this vulnerability by sending traffic to an affected device that has a maximum transmission unit (MTU) of 1800 bytes or greater. A successful exploit could allow the attacker to cause the device to reload.

  To exploit this vulnerability, the attacker may need access to the trusted network where the affected device is in order to send specific packets to be processed by the device. All network devices between the attacker and the affected device must support an MTU of 1800 bytes or greater. This access requirement could limit the possibility of a successful exploit.

  Cisco has released software updates that address this vulnerability. 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-qfp-ipsec-GQmqvtqV

  This advisory is part of the April 2022 release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: April 2022 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  At the time of publication, this vulnerability affected the following Cisco products if they were configured to terminate IPsec VPN connections and were running a vulnerable release of Cisco IOS XE Software that was running in autonomous or controller mode:

  • 1000 Series Integrated Services Routers 
  • 4221 Integrated Services Routers
  • 4321 Integrated Services Routers 
  • 4331 Integrated Services Routers 
  • 4351 Integrated Services Routers 
  • Catalyst 8200 Series Edge Platform
  • Catalyst 8300 Series Edge Platform

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

  Determine the Device Configuration

  A device that is running Cisco IOS XE Software is configured to terminate IPsec VPN connections. If one of the following conditions match, the device is affected:

  • A crypto map is configured for at least one interface
  • The device is configured with IPsec virtual tunnel interfaces (VTIs)

  The MTU of the interface that is used for encryption must also be increased to 1800 bytes or greater.

  To determine whether a crypto map is configured for at least one interface, use the show running-config | include ^interface|^ crypto map |^ mtu command. The following example shows a crypto map named map-group1 and increased MTU configured on the GigabitEthernet 0/0/0 interface:

  Router# show running-config | include ^interface|^ crypto map |^ mtu
   interface GigabitEthernet0/0/0
    mtu 1800
    crypto map map-group1

  To determine whether the device is configured with IPsec VTIs, use the show running-config | include ^interface|^ tunnel protection ipsec profile |^ mtu command and verify that the returned output contains tunnel protection ipsec profile configured under at least one tunnel interface and that the MTU has been increased on the physical interface associated to the tunnel. The following example shows VTI interface Tunnel1 and increased MTU on GigabitEthernet0/0/0:

  Router# show running-config | include ^interface|^ tunnel protection ipsec profile |^ mtu
  interface Tunnel1
   tunnel protection ipsec profile vti-1
  interface GigabitEthernet0/0/0
   mtu 1800

  Note: IPsec VPN is not configured by default.

  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 the following Cisco products:

  • IOS Software
  • IOS XR Software
  • Meraki products
  • NX-OS Software

Workarounds

• There is a workaround that addresses this vulnerability. Lower the MTU to less than 1800 bytes on all IPsec-enabled interfaces on affected devices by using the following command:

  Router(config-if)#mtu 1750

  Note: This will require changing the MTU on all peers of the IPsec connection.

  While this workaround has been deployed and proven successful in a test environment, customers should determine the applicability and effectiveness in their own environment and under their own use conditions. Customers should be aware that any workaround or mitigation that is implemented may negatively impact the functionality or performance of their network based on intrinsic customer deployment scenarios and limitations. Customers should not deploy any workarounds or mitigations before first evaluating the applicability to their own environment and any impact to such environment.

Fixed Software

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

  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.

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-qfp-ipsec-GQmqvtqV

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2022-APR-13

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