Summary

• A vulnerability in the ingress flow creation functionality of Cisco Adaptive Security Appliance (ASA) could allow an unauthenticated, remote attacker to cause the CPU to increase upwards of 100 percent utilization, causing a denial of service (DoS) condition on an affected system.
  
  The vulnerability is due to incorrect handling of an internal software lock that could prevent other system processes from getting CPU cycles, causing a high CPU condition. An attacker could exploit this vulnerability by sending a steady stream of malicious IP packets that can cause connections to be created on the targeted device. A successful exploit could allow the attacker to exhaust CPU resources, resulting in a DoS condition during which traffic through the device could be delayed. This vulnerability applies to either IPv4 or IPv6 ingress traffic either to or across an affected device.
  
  Cisco has released software updates that address this vulnerability. There are workarounds that address this vulnerability.
  
  This advisory is available at the following link:
  https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180418-asa2

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 2100 Series Security Appliances
  • Firepower 4110 Security Appliances
  • Firepower 9300 ASA Security Modules

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

  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.

  Determining the Cisco Firepower System Software Release

  To determine which Cisco Firepower System 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 Release 6.2.0:

  > show version
  
  ---------------------[ ftd ]---------------------
  Model : Cisco ASA5525-X Threat Defense (75) Version 6.2.0 (Build 362)
  UUID : 2849ba3c-ecb8-11e6-98ca-b9fc2975893c
  Rules update version : 2017-03-15-001-vrt
  VDB version : 279
  ----------------------------------------------------

  Products Confirmed Not Vulnerable

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

Workarounds

• The ASA and FTD configuration commands, set connection per-client-embryonic-max (TCP) and set connection per-client-max (TCP, UDP, and Stream Control Transmission Protocol {SCTP}), can be configured to limit the number of connection requests allowed. Using these configuration parameters can reduce the number of connections and greatly reduce the impact of the DoS attack.

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	First Fixed Release for This Vulnerability	Recommended Fixed Release for All the Vulnerabilities Described in the Collection of Advisories
  Prior to 9.11	Migrate to 9.1.7.20	9.1.7.20
  9.1	9.1.7.20	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 9.6.3.17	9.6.4.6
  9.6	9.6.3.17	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	9.9.1	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 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)
  6.0.1	Migrate to 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)
  6.1.0	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	6.2.0.5	6.2.0.5
  6.2.1	Migrate to 6.2.2.2	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	6.2.2.2	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 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 resolution of a Cisco TAC support case.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20180418-asa2

Revision History

• Version	Description	Section	Status	Date
  1.1	Explicitly stated that both to-the-box and transit traffic can trigger this condition. Clarified use case for the "per-client-max" limit.	Summary, Workarounds	Final	2018-April-23
  1.0	Initial public release.	—	Final	2018-April-18

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