Cisco ASA Software DNS Denial of Service Vulnerability

Summary

• A vulnerability in the DNS code of Cisco Adaptive Security Appliance (ASA) Software could allow an unauthenticated, remote attacker to cause an affected system to reload.
  
  The vulnerability is due to improper processing of DNS packets. An attacker could exploit this vulnerability by sending a request to an affected Cisco ASA appliance to cause it to generate a DNS request packet. The attacker would need to spoof the reply packet with a crafted DNS response.
  
  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.
  
  This vulnerability is documented in Cisco bug ID CSCut03495 (registered customers only) and has been assigned Common Vulnerabilities and Exposures (CVE) ID CVE-2015-6325.
  
  Cisco has released software updates that address this vulnerability. Workarounds that mitigate this vulnerability are not available. This advisory is available at the following link:
  http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20151021-asa-dns1

Affected Products

• Cisco ASA Software running on the following products is affected by this vulnerability:
  

  • Cisco Adaptive Security Virtual Appliance (ASAv)
  • 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

  
  See the "Fixed Software" section of this security advisory for more information about the affected releases.

  Vulnerable Products

  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 device 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 Version

  To determine whether a vulnerable version 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 version 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 version in the table that appears in the login window or the upper-left corner of the Cisco ASDM window.
  

  Products Confirmed Not Vulnerable

  Cisco FirePOWER 9300 ASA Security Module is not affected by this vulnerability.
  
  No other Cisco products are currently known to be affected by this vulnerability.

Indicators of Compromise

• No indicators of compromise are available for this vulnerability.

Workarounds

• There are no workarounds that mitigate this vulnerability. However, administrators may disable the affected feature.

Fixed Software

• When considering software upgrades, customers are advised to consult the Cisco Security Advisories and Responses archive at http://www.cisco.com/go/psirt and review subsequent advisories to determine exposure and a complete upgrade solution.
  
  In all cases, customers should ensure that the devices to upgrade 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.
  
  In the following table, the left column lists major releases of Cisco ASA Software. The center column indicates whether a major release is affected by the vulnerability described in this advisory and the first minor release that includes the fix for this vulnerability. The right column indicates whether a major release is affected by all the vulnerabilities described in the following advisories and which release includes fixes for those vulnerabilities:
  
  

  • cisco-sa-20151021-asa-dhcp1
  • cisco-sa-20150115-asa-dhcp
  • cisco-sa-20151021-asa-dns1
  • cisco-sa-20151021-asa-dns2
  • cisco-sa-20151021-asa-ike

  
  
  Customers should upgrade to an appropriate release as indicated in the following table:
  
  

  Cisco ASA Major Release	First Fixed Release for This Vulnerability	First Fixed Release for All Vulnerabilities Described in the October 2015 ASA Security Advisory Bundled Publication
  7.2	Affected; migrate to 8.2(5.58) or later	Affected; migrate to 8.2(5.58) or later
  8.2	8.2(5.58)	8.2(5.58) and later
  8.3	Affected; migrate to 8.4(7.29) or later	Affected; migrate to 8.4(7.29) or later
  8.4	8.4(7.29)	8.4(7.29)
  8.5	Affected; migrate to 9.0(4.37) or later	Affected; migrate to 9.0(4.37) or later
  8.6	Affected; migrate to 9.0(4.37) or later	Affected; migrate to 9.0(4.37) or later
  8.7	8.7(1.17)	8.7(1.17) and later
  9.0	9.0(4.37)	9.0(4.37) and later
  9.1	9.1(6.4)	9.1(6.8) and later
  9.2	9.2(4)	9.2(4) and later
  9.3	9.3(3.1)	9.3(3.5) and later
  9.4	9.4(1.1)	9.4(2) and later
  9.5	Not affected	Not affected

  
  
  

  Software Download

  Cisco ASA Software can be downloaded from the Software Center on Cisco.com by visiting http://www.cisco.com/cisco/software/navigator.html.
  
  For Cisco ASA 5500 Series Adaptive Security Appliances and Cisco ASA 5500-X Next Generation Firewall, navigate to the following path. To find interim versions, click All Releases > Interim on the left side of the download page.
  

  Products > Security > Firewalls > Adaptive Security Appliances (ASA) > ASA 5500 Series Adaptive Security Appliances > > Adaptive Security Appliance (ASA) Software

  For the Cisco ASA Services Module for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers, navigate to the following path. To find interim versions, click All Releases > Interim on the left side of the download page.
  

  Products > Cisco Interfaces and Modules > Services Modules > Catalyst 6500 Series / 7600 Series ASA Services Module > Adaptive Security Appliance (ASA) Software

  For the Cisco ASA 1000V Cloud Firewall, navigate to the following path:
  

  Products > Security > Firewalls > Adaptive Security Appliances (ASA) > ASA 1000V Cloud Firewall

  For the Cisco Adaptive Security Virtual Appliance (ASAv), navigate to the following path:
  

  Products > Security > Firewalls > Adaptive Security Appliances (ASA) > Adaptive Security Virtual Appliance (ASAv) > Adaptive Security Appliance (ASA) Software

  For the Cisco FirePOWER 9300 ASA Module, navigate to the following path:
  

  Products > Security > Firewalls > Adaptive Security Appliances (ASA) > Firepower 9000 Series > Firepower 9300 Security Appliance >Adaptive Security Appliance (ASA) Software

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 security tests.

URL

• http://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20151021-asa-dns1

Revision History

• Version	Description	Section	Status	Date
  1.1	Corrected recommended release version for Cisco ASA 9.3 train.	Fixed Software	Final	2015-November-12
  1.0	Initial public release.	-	Final	2015-October-21

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