Summary

• A vulnerability with the access control list (ACL) management within a stacked switch configuration of Cisco Business 250 Series Smart Switches and Business 350 Series Managed Switches could allow an unauthenticated, remote attacker to bypass protection offered by a configured ACL on an affected device.

  This vulnerability is due to incorrect processing of ACLs on a stacked configuration when either the primary or backup switches experience a full stack reload or power cycle. An attacker could exploit this vulnerability by sending crafted traffic through an affected device. A successful exploit could allow the attacker to bypass configured ACLs, causing traffic to be dropped or forwarded in an unexpected manner. The attacker does not have control over the conditions that result in the device being in the vulnerable state.

  Note: In the vulnerable state, the ACL would be correctly applied on the primary devices but could be incorrectly applied to the backup devices.

  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-sb-bus-acl-bypass-5zn9hNJk

Affected Products

• Vulnerable Products

  At the time of publication, this vulnerability affected the following Cisco products if they were running a vulnerable release of Cisco Small Business Firmware Software and were in a stacked configuration with ACLs configured:

  • 250 Series Smart Switches
  • 350 Series Managed Switches
  • 350X Series Stackable Managed Switches
  • 550X Series Stackable Managed Switches
  • Business 250 Series Smart Switches
  • Business 350 Series Managed Switches

  For information on the stackable configuration of Business Switches, see the Stacking Guidelines for Cisco Business Switches.

  For information about which Cisco software releases were vulnerable at the time of publication, see the Fixed Software section of this advisory. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.

  Products Confirmed Not Vulnerable

  Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.

Workarounds

• There are no workarounds that address this vulnerability.

  This vulnerability can leave the ACL configuration in an undefined state on the switch. As a mitigation, unbind the ACL from the non-working VLANs and then bind the ACL again. This is not a permanent mitigation. It would need to be reapplied if any switch stack member reloads or is power cycled.

  For the specific steps for unbinding and rebinding non-working ACLs, see the Cisco Business Switches 350 Series CLI Guide (pages 105 to 107) and the Cisco Business 350 Series Switches Administration Guide (pages 325 to 326). Contact the Cisco Technical Assistance Center (TAC) if further guidance is needed.

  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

• 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.

  Fixed Releases

  At the time of publication, the release information in the following tables was accurate. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.

  Business 250 Series Smart Switches and Business 350 Series Managed Switches

  Cisco Firmware Release	First Fixed Release
  3.4 and earlier	3.4.0.17

  250 Series Smart Switches, 350 Series Managed Switches, 350X Series Stackable Managed Switches, and 550X Series Stackable Managed Switches

  Cisco Firmware Release	First Fixed Release
  2.5 and earlier	2.5.9.54

  To download the firmware from the Software Center on Cisco.com, click Browse all and choose Switches > LAN Switches - Small Business.

  The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.

Exploitation and Public Announcements

• The Cisco 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-sb-bus-acl-bypass-5zn9hNJk

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2024-JAN-24

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