Summary

• A vulnerability in the data model interface (DMI) services of Cisco IOS XE Software could allow an unauthenticated, remote attacker to access resources that should have been protected by a configured IPv4 access control list (ACL).

  This vulnerability is due to improper handling of error conditions when a successfully authorized device administrator updates an IPv4 ACL using the NETCONF or RESTCONF protocol, and the update would reorder access control entries (ACEs) in the updated ACL. An attacker could exploit this vulnerability by accessing resources that should have been protected across an affected device.

  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-dmi-acl-bypass-Xv8FO8Vz

  This advisory is part of the March 2024 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: March 2024 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  At the time of publication, this vulnerability affected Cisco devices if they were running a vulnerable release of Cisco IOS XE Software and had the NETCONF or RESTCONF feature enabled to manage configured IPv4 ACLs. 

  The following ACL types are affected by this vulnerability:

  • IPv4 standard ACLs
  • IPv4 extended ACLs when they include ACEs with the log or log-input option

  IPv6 ACLs are not affected by this vulnerability.

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

  Determine the Device Configuration

  Both the NETCONF and RESTCONF features are disabled in Cisco IOS XE Software by default.

  Determine Whether NETCONF is Enabled

  To determine whether the NETCONF feature is enabled, use the show running-config | include netconf-yang CLI command. If the output of the command returns netconf-yang on a line by itself, the NETCONF feature is enabled, as shown in the following example:

  router#show running-config | include netconf-yang
  netconf-yang
  netconf-yang feature candidate-datastore
  router#

  If the output of this command is empty or does not contain netconf-yang on a line by itself, the NETCONF feature is disabled.

  Determine Whether RESTCONF is Enabled

  To determine whether the RESTCONF feature is enabled, use the show running-config | include restconf CLI command. If the output of the command returns restconf on a line by itself, the RESTCONF feature is enabled, as shown in the following example:

  router#show running-config | include restconf
  restconf
  router#

  If the output of this command is empty or does not contain restconf on a line by itself, the RESTCONF feature is disabled.

  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

Indicators of Compromise

• If the following messages are seen in the device logs, the device could be in a vulnerable state:

  %DMI-5-SYNC_NEEDED: R0/0: dmiauthd: Configuration change requiring running configuration sync detected - 'Failed to rollback configuration'. The running configuration will be synchronized  to the NETCONF running data store.
  %DMI-5-SYNC_START: R0/0: dmiauthd: Synchronization of the running configuration to the NETCONF running data store has started.
  %DMI-3-SYNC_ERR: R0/0: dmiauthd: An attempt to synchronize the running configuration to the NETCONF running data store has failed:
  %DMI-3-DMI_DEGRADED: R0/0: dmiauthd: The dmi infra is operating in degraded mode.  Most synchronizations from IOS to NETCONF datastore will not be performed

  If these logs are seen on a device, manually compare the current running-config to the expected configuration of the device, especially with regard to configured ACLs.

Workarounds

• There is a workaround that addresses this vulnerability.

  Manage ACLs directly on the device CLI instead of using the NETCONF or RESTCONF protocol.

  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.

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. This tool identifies any Cisco security advisories that impact a specific software release and the earliest release that fixes the vulnerabilities that are described in each advisory (“First Fixed”). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities that are described in all the advisories that the Software Checker identifies (“Combined First Fixed”). 

  To use the tool, go to the Cisco Software Checker page and follow the instructions. Alternatively, use the following form to determine whether a release is affected by any Cisco Security Advisory. To use the form, follow these steps:

  1. Choose which advisories the tool will search—only this advisory, only advisories with a Critical or High Security Impact Rating (SIR), or all advisories.
  2. Enter a release number—for example, 15.9(3)M2 or 17.3.3.
  3. Click Check.

   

  Only this advisory All Critical and High advisories All advisories

   

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

• Cisco would like to thank Andrej Mikus of Tronet for reporting this vulnerability.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-dmi-acl-bypass-Xv8FO8Vz

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2024-MAR-27

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