Summary

• A vulnerability in the DNS code of Cisco ASA Software could allow an unauthenticated, remote attacker to cause an affected device to reload or corrupt the information present in the device's local DNS cache.
  
  The vulnerability is due to a flaw in handling crafted DNS response messages. An attacker could exploit this vulnerability by triggering a DNS request from the Cisco ASA Software and replying with a crafted response. A successful exploit could cause the device to reload, resulting in a denial of service (DoS) condition or corruption of the local DNS cache information.
  
  Note: Only traffic directed to the affected device can be used to exploit this vulnerability. This vulnerability affects Cisco ASA Software configured in routed or transparent firewall mode and single or multiple context mode. This vulnerability can be triggered by IPv4 and IPv6 traffic.
  
  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-20170419-asa-dns

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco ASA Software running on the following products:
  

  • Cisco ASA 1000V Cloud Firewall
  • Cisco ASA 5500 Series Adaptive Security Appliances
  • Cisco ASA 5500-X Series Next-Generation Firewalls
  • Cisco ASA Services Module for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers
  • Cisco Adaptive Security Virtual Appliance (ASAv)
  • Cisco Firepower 9300 ASA Security Module
  • Cisco ISA 3000 Industrial Security Appliance

  Refer to the “Fixed Software” section of this security advisory for more information about affected releases.
  
  Cisco ASA Software is affected by this vulnerability if at least one DNS server IP address is configured under a DNS server group. This can be configured as part of the default DNS server group (DefaultDNS) or a user-defined DNS server group.
  
  To determine whether a DNS server IP address is configured, use the show running-config dns server-group command and verify that the name-server parameter includes an IP address.
  
  The following example shows a Cisco ASA Software appliance that is configured with the DNS server IP 192.168.1.1 as part of the DefaultDNS server group.
  

  ciscoasa# show running-config dns server-group
  
  DNS server-group DefaultDNS
      name-server 192.168.1.1
  .
  .
  .

  Note: By default, the DNS name-server value is not configured in any DNS server group.
  
  Determining the Running Software Release
  
  To determine whether a vulnerable release of Cisco ASA Software is running on an appliance, administrators can use the show version command. The following example shows the results for an appliance running Cisco ASA Software Release 9.2(1):

  ciscoasa# show version | include Version
  
  Cisco Adaptive Security Appliance Software Version 9.2(1) 
  Device Manager Version 7.4(1)

  Customers who use Cisco Adaptive Security Device Manager (ASDM) to manage devices can locate the software release in the table that appears in the login window or the upper-left corner of the Cisco ASDM window.

  Products Confirmed Not Vulnerable

  No other Cisco products are currently known to be affected by this vulnerability.

Workarounds

• There are no workarounds that address this vulnerability.

Fixed Software

• Cisco has released free software updates that address the vulnerability 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:
  http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.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:
  http://www.cisco.com/en/US/support/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.

  Fixed Releases

  In the following table, the left column lists major releases of Cisco ASA Software. The right column indicates whether a major release is affected by the vulnerability described in this advisory and the first release that includes the fix for this vulnerability.

  Cisco ASA Software Major Release	First Fixed Release
  Prior to 9.01	Affected, migrate to 9.1(7.12) or later
  9.01	Affected, migrate to 9.1(7.12) or later
  9.1	9.1(7.12) or later
  9.2	9.2(4.18) or later
  9.31	Affected, migrate to 9.4(3.12) or later
  9.4	9.4(3.12) or later
  9.5	9.5(3.2) or later
  9.6	9.6(2.2) or later
  9.7	Not affected
  9.8	Not affected

  
  ¹ Cisco ASA Software releases prior to 9.1 and Cisco ASA Software Release 9.3 have reached end-of-software maintenance. Customers should migrate to a supported release.
  
  Note: It is possible that certain fixed software releases for this vulnerability are affected by a bug described in Cisco Field Notice FN-64291 where a security appliance may fail to pass traffic after 213 days of uptime. Customers should review this notice before determining a course of action for addressing the vulnerability described in this advisory. The issue described in the Cisco Field Notice is not a security vulnerability.

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 internal testing.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170419-asa-dns

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2017-April-19

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