Summary

• Multiple vulnerabilities in the Zone-Based Firewall feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause the device to reload or stop forwarding traffic through the firewall.

  The vulnerabilities are due to incomplete handling of Layer 4 packets through the device. An attacker could exploit these vulnerabilities by sending a certain sequence of traffic patterns through the device. A successful exploit could allow the attacker to cause the device to reload or stop forwarding traffic through the firewall, resulting in a denial of service.

  For more information about these vulnerabilities, see the Details section of this advisory.

  Cisco has released software updates that address these vulnerabilities. There are no workarounds that address these vulnerabilities.

  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-zbfw-94ckG4G

  This advisory is part of the September 24, 2020, release of the Cisco IOS and IOS XE Software Security Advisory Bundled Publication, which includes 25 Cisco Security Advisories that describe 34 vulnerabilities. For a complete list of the advisories and links to them, see Cisco Event Response: September 2020 Semiannual Cisco IOS and IOS XE Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  These vulnerabilities affect devices that are running a vulnerable release of Cisco IOS XE Software and have the Zone-Based Firewall feature enabled with Layer 4 inspection enabled. The vulnerabilities are independent of each other.

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

  Determine the Device Configuration

  CVE-2020-3421

  The device is affected if the log dropped-packets feature is configured under the inspection parameter map. Administrators can validate this by logging into the device and using the show run | section parameter-map command. If the output contains any line with log dropped-packets, the device is vulnerable. The following examples show variations on a vulnerable configuration where the log dropped-packets feature is enabled either on the global inspect policy or on a custom-named inspect policy (if any of these appear in the configuration, the device is vulnerable):

  router_zbfw#show running-config | section parameter-map
  parameter-map type inspect cisco-sa-zbfw-94ckG4G
   log dropped-packets 
  router_zbfw#

  router_zbfw#show running-config | section parameter-map
  parameter-map type inspect-global
   log dropped-packets
  router_zbfw#

  router_zbfw#show running-config | section parameter-map
  parameter-map type inspect global
   log dropped-packets
  router_zbfw#

  CVE-2020-3480

  The device is affected if the one-minute high feature is configured under the inspection parameter map. Administrators can validate this by logging into the device and using the show run | section parameter-map command. If the output contains any line with one-minute high, the device is vulnerable. The following example shows variations on a vulnerable configuration where the one-minute high feature is enabled:

  router_zbfw#show running-config | section parameter-map
  parameter-map type inspect cisco-sa-zbfw-94ckG4G
   one-minute low 400
   one-minute high 500
  router_zbfw#

  
  

  Products Confirmed Not Vulnerable

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

  Cisco has confirmed that these vulnerabilities do not affect the following Cisco products:

  • IOS Software
  • IOS XR Software
  • NX-OS Software

Details

• The vulnerabilities are not dependent on one another. Exploitation of one of the vulnerabilities is not required to exploit the other vulnerability. In addition, a software release that is affected by one of the vulnerabilities may not be affected by the other vulnerability.

  Details about the vulnerabilities are as follows:

  CVE-2020-3421: Cisco IOS XE Software Zone-Based Firewall Denial of Service Vulnerability

  A vulnerability in the Zone-Based Firewall feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause the device to reload.

  The vulnerability is due to incomplete handling of Layer 4 packets through the device. An attacker could exploit this vulnerability by sending a certain sequence of traffic patterns through the device. A successful exploit could allow the attacker to cause the device to reload, resulting in a denial of service.

  Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.

  Bug ID(s): CSCvs71952
  CVE ID: CVE-2020-3421
  Security Impact Rating (SIR): High
  CVSS Base Score: 8.6
  CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X

  CVE-2020-3480: Cisco IOS XE Software Zone-Based Firewall Denial of Service Vulnerability

  A vulnerability in the Zone-Based Firewall feature of Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause the device to stop forwarding traffic through the firewall.

  The vulnerability is due to incomplete handling of Layer 4 packets through the device. An attacker could exploit this vulnerability by sending a certain sequence of traffic patterns through the device. A successful exploit could allow the attacker to cause the device to stop forwarding traffic through the firewall, resulting in a denial of service.

  Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability.

  Bug ID(s): CSCvt52986
  CVE ID: CVE-2020-3480
  Security Impact Rating (SIR): High
  CVSS Base Score: 8.6
  CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H/E:X/RL:X/RC:X

Workarounds

• There are no workarounds that address these vulnerabilities.

  For administrators that observe CVE-2020-3421, removing the log dropped-packets configuration until an upgrade can be performed is a viable mitigation.

Fixed Software

• Cisco has released free software updates that address the vulnerabilities described in this advisory. Customers may only install and expect support for software versions and feature sets for which they have purchased a license. By installing, downloading, accessing, or otherwise using such software upgrades, customers agree to follow the terms of the Cisco software license: https://www.cisco.com/c/en/us/products/end-user-license-agreement.html

  Additionally, customers may only download software for which they have a valid license, procured from Cisco directly, or through a Cisco authorized reseller or partner. In most cases this will be a maintenance upgrade to software that was previously purchased. Free security software updates do not entitle customers to a new software license, additional software feature sets, or major revision upgrades.

  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.

  Customers Without Service Contracts

  Customers who purchase directly from Cisco but do not hold a Cisco service contract and customers who make purchases through third-party vendors but are unsuccessful in obtaining fixed software through their point of sale should obtain upgrades by contacting the Cisco TAC: https://www.cisco.com/c/en/us/support/web/tsd-cisco-worldwide-contacts.html

  Customers should have the product serial number available and be prepared to provide the URL of this advisory as evidence of entitlement to a free upgrade.

  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 to identify 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 the Cisco Software Checker to search advisories in the following ways:

  • Choose the software and one or more releases
  • Upload a .txt file that includes a list of specific releases
  • Enter the output of the show version command

  After initiating a search, customers can customize the search to include all Cisco Security Advisories, a specific advisory, or all advisories in the most recent bundled publication.

  Customers can also use the following form to determine whether a release is affected by any Cisco Security Advisory by entering a Cisco IOS or IOS XE Software release-for example, 15.1(4)M2 or 3.13.8S:

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

  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 vulnerabilities that is described in this advisory.

Source

• These vulnerabilities were found during the resolution of a Cisco TAC support case.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-zbfw-94ckG4G

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2020-SEP-24

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