Summary

• A vulnerability in the Secure Sockets Layer (SSL) Virtual Private Network (VPN) Client Certificate Authentication feature for Cisco Adaptive Security Appliance (ASA) could allow an unauthenticated, remote attacker to establish an SSL VPN connection and bypass certain SSL certificate verification steps.
  
  The vulnerability is due to incorrect verification of the SSL Client Certificate. An attacker could exploit this vulnerability by connecting to the ASA VPN without a proper private key and certificate pair. A successful exploit could allow the attacker to establish an SSL VPN connection to the ASA when the connection should have been rejected.
  
  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://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180418-asa1

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco Adaptive Security Appliance (ASA) and Firepower Threat Defense (FTD) Software that is running on the following Cisco products:

  • 3000 Series Industrial Security Appliances (ISA)
  • ASA 5500 Series Adaptive Security Appliances
  • ASA 5500-X Series Next-Generation Firewalls
  • ASA Services Module for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers
  • Adaptive Security Virtual Appliances (ASAv)
  • Firepower 4110 Security Appliances
  • Firepower 9300 ASA Security Modules

  To be considered vulnerable, the ASA or FTD has to be configured for Client Certificate Authentication. Administrators can check for a vulnerable configuration using the show running-config tunnel-group | include authentication | include certificate command. If either the authentication certificate or authentication multiple-certificate configuration option is present in the configuration then the device is vulnerable. The following is an example of a vulnerable configuration:

  asa# show running-config tunnel-group | include authentication | include certificate
  authentication certificate
  authentication multiple-certificate

  Vulnerable ASA Software

  ASA Software is only vulnerable if running one of the following software versions:
  
  Release 9.4
  ASA software versions 9.4.3.1, 9.4.3.2 and 9.4.4 through 9.4.4.13
  
  Release 9.5
  ASA software versions 9.5.2.7, 9.5.2.8 and 9.5.3.7 through 9.5.3.9
  
  Release 9.6
  ASA software versions 9.6.2.9 through 9.6.2.21 and 9.6.3 through 9.6.3.17
  

  Determining the ASA Software Release

  To determine whether a vulnerable version of Cisco ASA Software is running on a device, administrators can use the show version | include Version command in the CLI. The following example shows the output of the command for a device that is running Cisco ASA Software Release 9.4(4):
  

  ciscoasa# show version | include Version
  Cisco Adaptive Security Appliance Software Version 9.4(4)
  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.

  Vulnerable FTD Software

  FTD software is only vulnerable if running one of the following software versions:
  
  Release 6.0
  FTD software versions 6.0 through 6.0.1.4.
  
  Release 6.1
  FTD software versions 6.1.0 through 6.1.0.5.
  

  Determining the Running FTD Software Release

  Administrators can use the show versionCLI command to determine the FTD release. In this example, the device is running software release 6.1.0.
  

  > show version
  ---------------------[ ftd ]---------------------
  Model : Cisco ASA5525-X Threat Defense (75) Version 6.1.0 (Build 362)
  UUID : 2849ba3c-ecb8-11e6-98ca-b9fc2975893c
  Rules update version : 2017-03-15-001-vrt
  VDB version : 279
  ----------------------------------------------------

  Products Confirmed Not Vulnerable

  Cisco has confirmed that this vulnerability does not affect Firepower 2100 Series Security Appliances.
  

  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 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.

  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

  Customers should upgrade to an appropriate release as indicated in the table(s) in this section. To help ensure a complete upgrade solution, consider that this advisory is part of a collection that includes the following advisories:
  

  • cisco-sa-20180418-asa1: Cisco Adaptive Security Appliance SSL Certificate Bypass Vulnerability
  • cisco-sa-20180418-asa2: Cisco Adaptive Security Appliance Flow Creation Denial of Service Vulnerability
  • cisco-sa-20180418-asa3: Cisco Adaptive Security Appliance TLS Denial of Service Vulnerability
  • cisco-sa-20180418-asaanyconnect: Cisco ASA Software, FTD Software, and AnyConnect Secure Mobility Client SAML Authentication Session Fixation Vulnerability
  • cisco-sa-20180418-asa_inspect: Cisco Adaptive Security Appliance Application Layer Protocol Inspection Denial of Service Vulnerability

  In the following table(s), the left column lists major releases of Cisco 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 this collection of advisories and the current recommended release for those vulnerabilities.

  ASA Software

  Cisco ASA Major Release	Recommended Fixed Release for This Vulnerability	Recommended Fixed Release for All the Vulnerabilities Described in the Collection of Advisories
  Prior to 9.11	Not vulnerable	9.1.7.20
  9.1	Not vulnerable	9.1.7.20
  9.2	Not vulnerable	9.2.4.27
  9.31	Not vulnerable	9.4.4.14
  9.4	9.4.4.14 or later	9.4.4.14
  9.51	Migrate to 9.6.3.20	9.6.4.6
  9.6	9.6.3.20 or later	9.6.4.6
  9.7	Not vulnerable	9.7.1.24
  9.8	Not vulnerable	9.8.2.28
  9.9	Not vulnerable	9.9.2.1

  ¹Cisco ASA Software releases prior to 9.1 and ASA releases 9.3 and 9.5 have reached End of Software Maintenance. Customers should migrate to a supported release.
  
  The software is available for download from Cisco Software Center by navigating to Products > Security > Firewalls > Adaptive Security Appliances (ASA) > ASA 5500-X Series Firewalls where there is a list of ASA hardware platforms. The majority of these software releases are listed under Interim.

  FTD Software

  Cisco FTD Major Release	Recommended Fixed Release for This Vulnerability	Recommended Fixed Release for All the Vulnerabilities Described in the Collection of Advisories
  6.0	Migrate to 6.1.0.6	Cisco_FTD_SSP_Hotfix_EI-6.1.0.7-2.sh (41xx and 9300 FTD hardware platform) Cisco_FTD_Hotfix_EI-6.1.0.7-2.sh (All FTD hardware platforms except 41xx and 9300)
  6.0.1	Migrate to 6.1.0.6	Cisco_FTD_SSP_Hotfix_EI-6.1.0.7-2.sh (41xx and 9300 FTD hardware platform) Cisco_FTD_Hotfix_EI-6.1.0.7-2.sh (All FTD hardware platforms except 41xx and 9300)
  6.1.0	6.1.0.6 or later	Cisco_FTD_SSP_Hotfix_EI-6.1.0.7-2.sh (41xx and 9300 FTD hardware platform) Cisco_FTD_Hotfix_EI-6.1.0.7-2.sh (All FTD hardware platforms except 41xx and 9300)
  6.2.0	Not vulnerable	6.2.0.5
  6.2.1	Not vulnerable	Cisco_FTD_SSP_Hotfix_BD-6.2.2.3-4.sh.REL.tar (41xx and 9300 FTD hardware platforms) Cisco_FTD_SSP_FP2K_Hotfix_BD-6.2.2.3-4.sh.REL.tar (21xx FTD hardware platform) Cisco_FTD_Hotfix_BD-6.2.2.3-4.sh.REL.tar (All other FTD hardware platforms)
  6.2.2	Not vulnerable	Cisco_FTD_SSP_Hotfix_BD-6.2.2.3-4.sh.REL.tar (41xx and 9300 FTD hardware platforms) Cisco_FTD_SSP_FP2K_Hotfix_BD-6.2.2.3-4.sh.REL.tar (21xx FTD hardware platform) Cisco_FTD_Hotfix_BD-6.2.2.3-4.sh.REL.tar (All other FTD hardware platforms)
  6.2.3	Not vulnerable	Cisco_FTD_SSP_Hotfix_A-6.2.3.1-10.sh.REL.tar (41xx and 9300 FTD hardware platforms) Cisco_FTD_SSP_FP2K_Hotfix_A-6.2.3.1-10.sh.REL.tar (21xx FTD hardware platform) Cisco_FTD_Hotfix_A-6.2.3.1-10.sh.REL.tar (All other FTD hardware platforms)

  
  The software is available for download from Cisco Software Center by navigating to Products > Security > Firewalls> Next-Generation Firewalls (NGFW) where there is a list of FTD hardware platforms.

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 resolved during resolution of a Cisco TAC Support case.

URL

• https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180418-asa1

Revision History

• Version	Description	Section	Status	Date
  1.1	Updated metadata. No text changes.	None	Final	2018-April-27
  1.0	Initial public release	—	Final	2018-April-18

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