Summary

• A vulnerability in the authentication, authorization, and accounting (AAA) function of Cisco IOS XE Software could allow an unauthenticated, remote attacker to bypass NETCONF or RESTCONF authentication and do either of the following:

  • Install, manipulate, or delete the configuration of an affected device
  • Cause memory corruption that results in a denial of service (DoS) on an affected device

  This vulnerability is due to an uninitialized variable. An attacker could exploit this vulnerability by sending a series of NETCONF or RESTCONF requests to an affected device. A successful exploit could allow the attacker to use NETCONF or RESTCONF to install, manipulate, or delete the configuration of a network device or to corrupt memory on the device, resulting a DoS.

  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-aaa-Yx47ZT8Q

  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 it is running in autonomous or controller mode and Cisco IOS XE SD-WAN Software. For either to be affected, all of the following must be configured:

  • AAA
  • NETCONF, RESTCONF, or both
  • enable password without enable secret

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

  Note: The standalone Cisco IOS XE SD-WAN release images are separate from the universal Cisco IOS XE Software releases. The SD-WAN feature set was first integrated into the universal Cisco IOS XE Software releases starting with IOS XE Software Release 17.2.1r. For additional information, see the Install and Upgrade Cisco IOS XE Release 17.2.1r and Later chapter of the Cisco SD-WAN Getting Started Guide.

  Determine the Device Configuration

  To determine whether a device has a vulnerable configuration, do the following:

  Check AAA Configuration

  To determine whether AAA authentication is configured on the device, use the show running-config | include aaa authentication login command, as shown in the following example:

  Router#show running-config | include aaa authentication login
  aaa authentication login default local group example
  Router#

  Check NETCONF and RESTCONF Configuration

  To determine whether NETCONF or RESTCONF is configured on the device, use the show running-config | include netconf|restconf command, as shown in the following example:

  Router#show running-config | include netconf|restconf
  netconf-yang
  restconf
  Router#

  Check enable password Configuration

  To determine whether enable password is configured on the device without the presence of an enable secret, use the show running-config | include enable password|secret command, as shown in the following example:

  Router#show running-config | include enable password|secret
  enable password 7 00010B07094B0703
  Router#

  Note: If enable secret is being used without the presence of enable password, the device is not affected.

  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: Remove the enable password and configure an enable secret. For more information, see Cisco Guide to Harden Cisco IOS Devices.

  There is also a mitigation that addresses this vulnerability: To limit the attack surface of this vulnerability, ensure that access control lists (ACLs) are in place for NETCONF and RESTCONF to prevent attempted access from untrusted subnets. For more information, see NETCONF and RESTCONF Service-Level ACLs.

  While this workaround and this mitigation have been deployed and were 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-aaa-Yx47ZT8Q

Revision History

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

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