Summary

• A vulnerability in the UDP forwarding code of Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to bypass configured management plane protection policies and access the Simple Network Management Plane (SNMP) server of an affected device.

  This vulnerability is due to incorrect UDP forwarding programming when using SNMP with management plane protection. An attacker could exploit this vulnerability by attempting to perform an SNMP operation using broadcast as the destination address that could be processed by an affected device that is configured with an SNMP server. A successful exploit could allow the attacker to communicate to the device on the configured SNMP ports. Although an unauthenticated attacker could send UDP datagrams to the configured SNMP port, only an authenticated user can retrieve or modify data using SNMP requests.

  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-snmp-uhv6ZDeF

  This advisory is part of the March 2024 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: March 2024 Semiannual Cisco IOS XR 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 XR Software and had management plane protection configured with the SNMP server enabled.

  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.

  Determine Whether Management Plane Protection is Configured

  To determine whether management plane protection is configured, enter the command show running-config control-plane management-plane. If the command returns output, management plane protection is configured, as shown in the following example:

  Router# show running-config control-plane management-plane
  !
  control-plane
   management-plane
    inband
     interface all
      allow SSH
     !
    !
   !
  !
  Router#

  Determine Whether SNMP Server is Configured

  To determine whether the SNMP server is configured, enter the command show running-config snmp. The device can be configured with either SNMPv2c or SNMPv3. If the command returns output, SNMP server is configured, as shown in the following example:
  

  Router# show running-config snmp-server
  !
  snmp-server community example RO
  !
  Router#

  
  

  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

• Exploitation of this vulnerability could allow an attacker to bypass protections that are provided by an access control list (ACL) that is applied on an affected device. The overall impact of exploitation is organization-specific because it depends on the importance of the assets that the ACL was supposed to protect. Customers should evaluate how exploitation of this vulnerability would impact their network and proceed according to their own vulnerability-handling and remediation processes.

Workarounds

• There is a workaround that addresses this vulnerability.

  Disable UDP forwarding

  UDP forwarding is enabled by default for DNS, TFTP, TACACS, IEN 116 Name Service, NetBIOS Name Service (NBNS), and NetBIOS Datagram Service (NBDS) protocols. UDP forwarding is not enabled by default for other UDP protocols.

  If UDP forwarding is not required, a workaround is to disable UDP forwarding globally by using the forward-protocol udp disable command as shown in the following example:

  RP/0/RSP0/CPU0:ios#configure terminal
  RP/0/RSP0/CPU0:ios(config)#forward-protocol udp disable
  RP/0/RSP0/CPU0:ios(config)#commit

  Note: If UDP broadcast forwarding is required for any default protocol or if UDP broadcast forwarding has been configured with the forward-protocol udp <port number> command, this workaround cannot be used.

  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.

  Fixed Releases

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

  The left column lists Cisco software releases, and the right column indicates whether a release was affected by the vulnerability described in this advisory and which release included the fix for this vulnerability.

  Cisco IOS XR Software Release	First Fixed Release
  7.11 and earlier	Migrate to a fixed release.
  24.1	24.1.1

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

  Cisco has not released SMUs to address this vulnerability.

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-snmp-uhv6ZDeF

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2024-MAR-13

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