Summary

• A vulnerability in the Rate Limiting Network Address Translation (NAT) feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause high CPU utilization in the Cisco QuantumFlow Processor of an affected device, resulting in a denial of service (DoS) condition.

  This vulnerability is due to mishandling of the rate limiting feature within the QuantumFlow Processor. An attacker could exploit this vulnerability by sending large amounts of traffic that would be subject to NAT and rate limiting through an affected device. A successful exploit could allow the attacker to cause the QuantumFlow Processor utilization to reach 100 percent on the affected device, resulting in a DoS condition.

  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-ratenat-pYVLA7wM

  This advisory is part of the September 2021 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: September 2021 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco IOS XE Software if the Rate Limiting NAT feature is enabled.

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

  Determine the Device Configuration

  To determine whether the Rate Limiting NAT feature is enabled, use the show running-config | include ip nat translation max-entries CLI command. If the command returns output, as shown in the following example, the Rate Limiting NAT feature is enabled:

  Router# show running-config | include ip nat translation max-entries
  ip nat translation max-entries 
  ip nat translation max-entries all-host 
  Router#

  
  

  Determine the Available Sub-Commands

  The Rate Limiting NAT feature supports several sub-commands. The following max-entries sub-commands have been fixed as part of this investigation:

  • ip nat translation max-entries
  • ip nat translation max-entries all-host
  • ip nat translation max-entries host

  The remaining max-entries configuration sub-commands are affected by the vulnerability that is described in this advisory and is documented in Cisco Bug ID CSCvx75321. Cisco does not plan to fix these sub-commands.

  To determine whether the sub-commands that have been fixed are enabled on an affected device, use the show running-config | include ^ip nat translation max-entries (all-host|host|[0-9]) CLI command. If the command returns output, upgrading to a fixed software release is recommended.

  To determine whether the commands that have not been fixed are enabled, use the show running-config | include ^ip nat translation max-entries (all-vrf|list|redundancy|vrf) CLI command. If the command returns output, the device is considered vulnerable. Administrators should consider removing those commands.

  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

Details

• To show the QuantumFlow Processor utilization, use the command show platform hardware qfp active data utilization, as shown in the following example:

  Router#show platform hardware qfp active data utilization summary
    CPP 0:                    5 secs       1 min       5 min      60 min
  Input:     Total (pps)       44150       44158       41901        8720
                   (bps)    49446512    49455192    46928320     9765272
  Output:    Total (pps)           8           9           9           4
                   (bps)       12016       15656       15120        9224
  Processing: Load (pct)          99          99          53           8

Workarounds

• There are no workarounds that address this vulnerability. However, as a mitigation, administrators can remove all ip nat translation max-entries commands from the configuration.

  While this mitigation has been deployed and was 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

• 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 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.

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-ratenat-pYVLA7wM

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2021-SEP-22

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