Summary

• Cisco IOS XR Software supports a programmatic way of configuring and collecting operational data on a network device using data models. Data models provide access to the capabilities of the devices in a network using NETCONF or gRPC.

  According to Cisco IOS XR Software configuration guides, if NETCONF or gRPC are enabled on a device, authentication, authorization, and accounting (AAA) authorization should be configured to prevent unauthorized access:

  Configure AAA authorization to restrict users from uncontrolled access. If AAA authorization is not configured, the command and data rules associated to the groups that are assigned to the user are bypassed. An IOS-XR user can have full read-write access to the IOS-XR configuration through Network Configuration Protocol (NETCONF), google-defined Remote Procedure Calls (gRPC) or any YANG-based agents. In order to avoid granting uncontrolled access, enable AAA authorization using aaa authorization exec command before setting up any configuration

  This informational advisory describes the impact of not having AAA authorization configured on a device when NETCONF or gRPC (gRPC Network Management Interface or gRPC Network Operations Interface) are configured.

  This advisory is available at the following link:

  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxr-info-GXp7nVcP

  
  

  This advisory is part of the September 2023 release of the Cisco IOS XR Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: September 2023 Semiannual Cisco IOS XR Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This informational advisory pertains to Cisco IOS XR Software and Cisco IOS XR7 (LNT) when they support and are configured with either NETCONF or gRPC. If AAA is not enabled, task-based access control may not be enforced.

  Determine Whether NETCONF and gRPC Are Configured

  To determine whether a device that is running Cisco IOS XR Software is configured to use either NETCONF or gRPC, use the show running-config netconf-yang agent and show running-config grpc CLI commands. If either command returns output, as shown in the following example, the corresponding protocol is enabled:

  RP/0/RP0/CPU0:8101-A#show running-config netconf-yang agent
  Sun Mar  5 23:18:28.756 UTC 
  netconf-yang agent 
   ssh
  !
  
  RP/0/RP0/CPU0:8101-A#show running-config grpc
  Sun Mar  5 23:18:38.070 UTC
  grpc
   port 57400
  !
  
  RP/0/RP0/CPU0:8101-A#
  

  Determine Whether AAA Authorization EXEC Is Configured

  To determine whether a device that is running Cisco IOS XR Software is configured with AAA authorization EXEC, use the show running-config aaa authorization CLI command. If the command returns output similar to what is shown in the following example, AAA authorization EXEC is enabled (in this case, with the default method):

  RP/0/RSP0/CPU0:SR1#show running-config aaa authorization
  Sun Mar  5 23:44:05.479 UTC
  aaa authorization exec default local
  
  RP/0/RSP0/CPU0:SR1#

  If AAA authorization EXEC is not configured on a device but NETCONF, gRPC, or both are configured on the device, there are implications. For more information on these implications, see the Details section of this advisory.

  Note: NETCONF supports the NETCONF Access Control Model (NACM), which is configured using the aaa authorization nacm CLI command. If both NETCONF and NACM authorization are enabled on a device, and gRPC is not enabled, then AAA authorization EXEC is not required to address the issue described in this advisory.

  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 XE Software
  • NX-OS Software

Details

• Cisco recommends that customers review their AAA configurations if they are using NETCONF or gRPC and ensure that AAA authorization EXEC is configured to prevent the security issue that is described in this advisory.

  NETCONF Behavior

  The client establishes a NETCONF session over SSH to the NETCONF Agent. If AAA authorization EXEC is configured, the configured method list is returned. If AAA authorization EXEC is not configured, the default method list is returned.

  In Cisco IOS XR7 (LNT), if AAA authorization EXEC is not configured, authorization is skipped. This issue is addressed by Cisco Bug CSCwe35622.

  The following table summarizes task-based authorization enforcement with NETCONF:

  Cisco IOS XR Software	Is Task-Based Authorization Enforced?
  		Without AAA	With AAA login authentication, but no AAA authorization EXEC	With AAA authorization EXEC	With default NACM	With configured NACM
  Cisco IOS XR (32-bit)	Not enforced.	Not enforced.	Enforced.	Enforced.	Enforced.
  Cisco IOS XR (64-bit)	Release 7.1.1 and earlier: Not enforced. Release 7.1.2 and later: Enforced.	Release 7.1.1 and earlier: Not enforced. Release 7.1.2 and later: Enforced.	Enforced.	Enforced.	Enforced.
  Cisco IOS XR7 (LNT)	Not enforced; requires CSCwe35622 fix.	Not enforced; requires CSCwe35622 fix.	Enforced.	Enforced.	Enforced.

  Note: NETCONF only supports the default method list; therefore, customers should ensure that aaa authorization exec default is configured on their device.

  gRPC Behavior

  The client establishes a gRPC session through the mgbl Extensible Manageability Services (EMSd) process on Cisco IOS XR Software, then is passed to the YANG framework (YFW) encode/decode layer. EMSd does not pass task map information to the YFW. As a workaround, the YFW process calls AAA for authorization, but it needs to be instructed to do this using AAA authorization EXEC. If AAA authorization EXEC is not configured, authorization is skipped for gRPC sessions.

  Cisco plans to address this issue with new service-level and path-level authorization mechanisms in the future.

  The following table summarizes task-based authorization enforcement with gRPC:

  Cisco IOS XR Software	Is Task-Based Authorization Enforced?
  		Without AAA	With AAA login authentication but no AAA authorization EXEC	With AAA authorization EXEC
  IOS XR (32-bit)	Not supported.	Not supported.	Not supported.
  IOS XR (64-bit)	Not enforced.	Not enforced.	Enforced.
  IOS XR7 (LNT)	Not enforced.	Not enforced.	Enforced.

  Note: gRPC supports named method lists. If a device is using an authorization method name other than default, ensure grpc aaa authorization exec and aaa authorization exec match.

Workarounds

• There is a workaround that addresses this vulnerability.

  Review the device configuration and ensure that when NETCONF or gRPC are being used, AAA authorization EXEC (or NACM for NETCONF) is enabled.

  While this workaround 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.

Exploitation and Public Announcements

• The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the issue that is described in this advisory.

Source

• This issue was found during internal security testing.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-iosxr-info-GXp7nVcP

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2023-SEP-13

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