Summary

• A vulnerability in access control list (ACL) functionality of the Gigabit Ethernet Management interface of Cisco IOS XE Software could allow an unauthenticated, remote attacker to reach the configured IP addresses on the Gigabit Ethernet Management interface.

  The vulnerability is due to a logic error that was introduced in the Cisco IOS XE Software 16.1.1 Release, which prevents the ACL from working when applied against the management interface. An attacker could exploit this issue by attempting to access the device via the management interface.

  Cisco has released software updates that address this vulnerability. There are partial workarounds that address this vulnerability.

  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190327-mgmtacl

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco devices that are running a vulnerable 16.x release of Cisco IOS XE Software and are configured with an access control list (ACL) on the Gigabit Ethernet Management interface. This vulnerability was introduced in Cisco IOS XE Software Release 16.1.1.

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

  Assessing the Gigabit Ethernet Management Interface

  To determine whether the Gigabit Ethernet Management interface configuration is affected, administrators can log in to the device and use the show running-config | section interface GigabitEthernet0$ command in the CLI to check for the presence of the ip access-group command or the ipv6 traffic-filter command. If either command is present and configured, the device has an affected configuration.

  The following example shows the output of the show running-config | section interface GigabitEthernet0$ command for a router that has an affected configuration:

  Router# sh running-config | section interface GigabitEthernet0$
  interface GigabitEthernet0
   vrf forwarding Mgmt-intf
   ip address 192.168.1.1 255.255.255.0
   ip access-group 100 in

  Determining the Cisco IOS XE Software Release

  To determine which Cisco IOS XE Software release is running on a device, administrators can log in to the device, use the show version command in the CLI, and then refer to the system banner that appears. If the device is running Cisco IOS XE Software, the system banner displays Cisco IOS Software, Cisco IOS XE Software, or similar text.

  The following example shows the output of the command for a device that is running Cisco IOS XE Software Release 16.2.1 and has an installed image name of CAT3K_CAA-UNIVERSALK9-M:

  ios-xe-device# show version
  
  Cisco IOS Software, Catalyst L3 Switch Software (CAT3K_CAA-UNIVERSALK9-M), Version Denali 16.2.1, RELEASE SOFTWARE (fc1)
  Technical Support: http://www.cisco.com/techsupport
  Copyright (c) 1986-2016 by Cisco Systems, Inc.
  Compiled Sun 27-Mar-16 21:47 by mcpre
  .
  .
  .

  For information about the naming and numbering conventions for Cisco IOS XE Software releases, see the Cisco IOS and NX-OS Software Reference Guide.

  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 Cisco IOS Software, Cisco IOS XR Software, or Cisco NX-OS Software.

Details

• If an access list is applied to the Gigabit Ethernet Management interface, it is not evaluated from Cisco IOS XE Software Release 16.1.1 until the first fix, resulting in the ACL being bypassed.

  All platforms are addressed under Cisco Bug ID CSCvk47405 with the exception of Cisco Catalyst 9200 Series Switches, which are addressed under Cisco Bug ID CSCvm97704.

Workarounds

• For features that leverage the TTYs, administrators can apply an access control list to all VTY lines, which will mitigate this vulnerability for those applications as shown in the following example:

  !
  ! Create the Access Control List
  !
  ip access-list standard Mgmt-Int-ACL
   remark *** Allow Trusted Hosts ***
   permit 192.168.0.1
   remark *** Deny all Others ***
   deny   any
  !
  ! Applied the ACL to the VTY lines
  !
  line vty 0 4
   access-class Mgmt-Int-ACL in
  !
  ! Applied to the http server (if enabled)
  !
  ip http access-class ipv4 Mgmt-Int-ACL
  
  

  Applications that are accessible on the device but do not use the TTYs application-specific ACLs (where supported) would have to be configured. One example is if the HTTP server is enabled. To apply an HTTP server ACL, see the following example:

  !
  ! Create the Access Control List
  !
  ip access-list standard Mgmt-Int-ACL
   remark *** Allow Trusted Hosts ***
   permit 192.168.0.1
   remark *** Deny all Others ***
   deny   any
  !
  ! Applied to the http server (if enabled)
  !
  ip http access-class ipv4 Mgmt-Int-ACL
  
  

  Applications that are accessible on the device that do not require a TTY to be allocated and do not support application-specific ACLs are still exposed. Two examples are TFTP and FTP.

Fixed Software

• For detailed information about affected and fixed software releases, consult the Cisco IOS Software Checker.

  When considering software upgrades, customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories and Alerts 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 a tool, the Cisco IOS Software Checker, that identifies 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 this tool to perform the following tasks:

  • Initiate a search by choosing one or more releases from a drop-down list or uploading a file from a local system for the tool to parse
  • Enter the output of the show version command for the tool to parse
  • Create a custom search by including all previously published Cisco Security Advisories, a specific advisory, or all advisories in the most recent bundled publication

  To determine whether a release is affected by any published Cisco Security Advisory, use the Cisco IOS Software Checker on Cisco.com or enter a Cisco IOS or IOS XE Software release-for example, 15.1(4)M2 or 3.13.8S-in the following field:

  By default, the Cisco IOS Software Checker includes results only for vulnerabilities that have a Critical or High Security Impact Rating (SIR). To include results for Medium SIR vulnerabilities, use the Cisco IOS Software Checker on Cisco.com and check the Medium check box in the Impact Rating drop-down list.

  For a mapping of Cisco IOS XE Software releases to Cisco IOS Software releases, refer to the Cisco IOS XE 2 Release Notes, Cisco IOS XE 3S Release Notes, or Cisco IOS XE 3SG Release Notes, depending on the Cisco IOS XE Software release.

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-20190327-mgmtacl

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2019-March-27

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