Cisco Adaptive Security Appliance TLS Denial of Service Vulnerability

Summary

• A vulnerability in the Transport Layer Security (TLS) library of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to trigger a reload of the affected device, resulting in a denial of service (DoS) condition.
  
  The vulnerability is due to insufficient validation of user-supplied input. An attacker could exploit this vulnerability by sending a malicious TLS message to an interface enabled for Secure Layer Socket (SSL) services on an affected device. Messages using SSL Version 3 (SSLv3) or SSL Version 2 (SSLv2) cannot be be used to exploit this vulnerability. An exploit could allow the attacker to cause a buffer underflow, triggering a crash on an affected device.
  
  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-asa3

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco ASA Software and Cisco FTD Software that is running on the following Cisco products:
  

  • Adaptive Security Virtual Appliance (ASAv)
  • Firepower Threat Defense Virtual (FTDv)
  • Firepower 2100 Series Security Appliance

  ASA Software

  Cisco ASA Software is only vulnerable if running software version 9.2 or later.
  
  In the following table, the left column lists the vulnerable Cisco ASA features. The right column indicates the vulnerable configuration from the CLI command show running-config, if it can be determined.
  
  

  Feature	Vulnerable Configuration
  Adaptive Security Device Manager (ASDM)1	http server enable http
  AnyConnect SSL VPN	webvpn enable
  Cisco Security Manager2	http server enable http
  Clientless SSL VPN	webvpn enable
  Mobile User Security (MUS)	webvpn mus password mus server enable port mus
  Security Assertion Markup Language (SAML) Single Sign-On (SSO)3	N/A

  ¹ ASDM is vulnerable only from an IP address in the configured http command range.
  ² Cisco Security Manager is vulnerable only from an IP address in the configured http command range.
  ³ SAML SSO is first supported as of software release 9.6.

  Determining the Cisco ASA Software Release

  To determine whether a vulnerable version of Cisco ASA Software is running on a device, administrators can use the show version command in the CLI. The following example shows the output of the command for a device that is running Cisco ASA Software Release 9.7(1)4:
  

  ciscoasa# show version | include Version
  Cisco Adaptive Security Appliance Software Version 9.7(1)4
  Firepower Extensible Operating System Version 2.1(1.66)
  Baseboard Management Controller (revision 0x1) Firmware Version: 2.4

  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.

  FTD Software

  The FTD Software is only vulnerable if running software versions 6.0, 6.0.1, 6.1.0, 6.2.1, or 6.2.2 prior to their respective first fixed releases.
  
  In the following table, the left column lists the vulnerable Cisco FTD features. The right column indicates the vulnerable configuration from the CLI command show running-config, if it can be determined.
  
  

  Feature	Vulnerable Configuration
  HTTP Service enabled1	http server enable http
  AnyConnect SSL VPN2,3	webvpn enable

  ¹ The HTTP feature is enabled via the Firepower Threat Defense Platform Settings > HTTP configuration page on the Firepower Management Console (FMC).
  ² Remote Access VPN features are enabled via the Devices > VPN > Remote Access configuration page on the FMC or via the Device > Remote Access VPN configuration page on the Firepower Device Manager (FDM).
  ³ Remote Access VPN features are first supported as of software release 6.2.1.

  Determining the Cisco FTD Software Release

  To determine which Cisco FTD Software release is running on a device, administrators can log in to the device and use the show version command in the CLI. The following example shows the output of the command for a device that is running Cisco FTD Software Release 6.2.2:

  > show version
  
  ------------------[ ftd ]-----------------------
  Model : Cisco Firepower 2130 Threat Defense (77) Version 6.2.2 (Build 81)
  UUID : 0cd3595a-7efa-11e7-aaa1-ee3989c8bf25
  Rules update version : 2017-12-20-001-vrt
  VDB version : 290
  ----------------------------------------------------

  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:
  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.

  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	First Fixed Release for This Vulnerability	Recommended Fixed Release for All the Vulnerabilities Described in this Collection of Advisories
  Prior to 9.11	Not vulnerable	9.1.7.20
  9.1	Not vulnerable	9.1.7.20
  9.2	9.2.4.27	9.2.4.27
  9.31	Migrate to 9.4.4.13	9.4.4.14
  9.4	9.4.4.13	9.4.4.14
  9.51	Migrate to 9.6.3.20	9.6.4.6
  9.6	9.6.3.20	9.6.4.6
  9.7	9.7.1.16	9.7.1.24
  9.8	9.8.2.14	9.8.2.28
  9.9	Not vulnerable	9.9.2.1

  
  ¹ Cisco 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	First Fixed Release for This Vulnerability	Recommended Fixed Release for All the Vulnerabilities Described in this 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	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 vulnerable1	6.2.0.5
  6.2.1	Migrate to 6.2.2.1	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	6.2.2.1	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)

  
  ¹ Cisco FTD Software release 6.2.0 introduced a new HTTP server and thus the attack vector via the HTTP Service no longer applies.
  
  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 possible 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 found during the resolution of a Cisco TAC support case.

URL

• https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180418-asa3

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2018-April-18

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