Summary

• A vulnerability in the WebVPN login process of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause increased CPU utilization on an affected device.

  The vulnerability is due to excessive processing load for existing WebVPN login operations. An attacker could exploit this vulnerability by sending multiple WebVPN login requests to the device. A successful exploit could allow the attacker to increase CPU load on the device, resulting in a denial of service (DoS) condition.

  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-20190501-sd-cpu-dos

Affected Products

• Vulnerable Products

  This vulnerability affects the following Cisco products that are running Cisco ASA Software or FTD Software when configured for WebVPN:

  • 3000 Series Industrial Security Appliances (ISAs)
  • Adaptive Security Appliance (ASA) 1000V Cloud Firewall
  • ASA 5505 Series Adaptive Security Appliance¹
  • ASA 5500-X Series Firewalls
  • ASA Services Module for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers
  • Adaptive Security Virtual Appliance (ASAv)
  • Firepower 2100 Series
  • Firepower 4100 Series
  • Firepower 9300 ASA Security Module
  • Firepower Threat Defense Virtual

  ¹ASA 5500 Series Adaptive Security Appliances other than the ASA 5505 have reached the end-of-support milestone and are no longer evaluated for security vulnerabilities.

  For information about which Cisco ASA Software and FTD Software releases are vulnerable, see the Fixed Software section of this advisory.

  Determining If WebVPN Is Enabled

  To determine if the WebVPN service is enabled on a device, administrators can use the show running-config webvpn privileged EXEC command and refer to the output of the command. The following example shows the output of the command for a device that has the WebVPN service enabled:

  ciscoasa# show running-config webvpn

  .
  .
  .
  webvpn
  enable interface_name
  .
  .
  .

  Determining the Cisco ASA Software Release

  To determine which Cisco ASA Software release is running on a device, administrators can log in to the device, use the show version | include Version command in the CLI, and refer to the output of the command. The following example shows the output of the command for a device that is running Cisco ASA Software Release 9.9.2.18:

  ciscoasa# show version | include Version
  Cisco Adaptive Security Appliance Software Version 9.9.2.18
  Device Manager Version 7.4(1)
  .
  .
  .

  If a device is managed by using Cisco Adaptive Security Device Manager (ASDM), administrators can also determine which release is running on a device by referring to the release information in the table that appears in the Cisco ASDM login window or the Device Dashboard tab of the Cisco ASDM Home pane.

  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, use the show version command in the CLI, and refer to the output of the command. The following example shows the output of the command for a device that is running Cisco FTD Software 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

  Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability.

Indicators of Compromise

• During active exploitation of this vulnerability, administrators may notice increased CPU usage by the Unicorn Proxy Thread process. This can be checked by issuing the show processes cpu-usage non-zero command at the CLI and reviewing the statistics for the Unicorn Proxy Thread process.

  ciscoasa# show processes cpu-usage non-zero
  Hardware:   ASA5516
  Cisco Adaptive Security Appliance Software Version 9.8(2)38
  ASLR enabled, text region 7f313ea71000-7f3142d61bb4
  PC         Thread       5Sec     1Min     5Min   Process
  0x00007f3140f35888   0x00002aaacfaa8b20     7.7%     5.0%     3.0%   Unicorn Proxy Thread
     -          -         9.5%     1.9%     0.8%   DATAPATH-0-2044
     -          -         3.6%     1.4%     0.8%   DATAPATH-1-2045
  

  It should be noted that the previous output is an example. Administrators would need to compare the output values from their device to baseline values from normal device operation.

Workarounds

• There are no workarounds that address this vulnerability.

  It is possible that during active exploitation an administrator could mitigate the attack by implementing an ACL to block the incoming requests or perform rate-limiting.

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 are advised to upgrade to an appropriate release as indicated in the applicable table in this section. To ensure a complete upgrade solution, customers should consider that this advisory is part of a collection that includes the following advisories:

  • cisco-sa-20190501-asa-csrf: Cisco Adaptive Security Appliance Software Cross-Site Request Forgery Vulnerability
  • cisco-sa-20190501-asa-frpwrtd-dos: Cisco Adaptive Security Appliance Software and Cisco Firepower Threat Defense Software TCP Timer Handling Denial of Service Vulnerability
  • cisco-sa-20190501-asa-ftd-dos: Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software WebVPN Denial of Service Vulnerability
  • cisco-sa-20190501-asa-ftd-entropy: Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software Low-Entropy Keys Vulnerability
  • cisco-sa-20190501-asa-ftd-ike-dos: Cisco Adaptive Security Appliance Software and Cisco Firepower Threat Defense Software MOBIKE Denial of Service Vulnerability
  • cisco-sa-20190501-asaftd-saml-vpn: Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software VPN SAML Authentication Bypass Vulnerability
  • cisco-sa-20190501-asa-ipsec-dos: Cisco Adaptive Security Appliance Software IPsec Denial of Service Vulnerability
  • cisco-sa-20190501-firepower-dos: Cisco Firepower Threat Defense Software TCP Ingress Handler Denial of Service Vulnerability
  • cisco-sa-20190501-frpwr-dos: Cisco Firepower Threat Defense Software Packet Processing Denial of Service Vulnerability
  • cisco-sa-20190501-frpwr-smb-snort: Cisco Firepower Threat Defense Software SMB Protocol Preprocessor Detection Engine Denial of Service Vulnerabilities
  • cisco-sa-20190501-sd-cpu-dos: Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software WebVPN Denial of Service Vulnerability

  In the following table(s), the left column lists Cisco software releases. The center column indicates whether a release is affected by the vulnerability described in this advisory and the release that includes the fix for this vulnerability. The right column indicates whether a release is affected by all the vulnerabilities described in this collection of advisories and which release includes fixes for those vulnerabilities.

  Cisco ASA Software

  Cisco ASA Software Release	Recommended Release for This Vulnerability	Recommended Release for All the Vulnerabilities Described in the Collection of Advisories
  Prior to 9.41	9.4.4.34	9.4.4.34
  9.4	9.4.4.34	9.4.4.34
  9.51	9.6.4.25	9.6.4.25
  9.6	9.6.4.25	9.6.4.25
  9.7	9.8.4	9.8.4
  9.8	9.8.4	9.8.4
  9.9	9.9.2.50	9.9.2.50
  9.10	Not vulnerable	9.10.1.17
  9.12	Not vulnerable	Not vulnerable

  ¹Cisco ASA Software releases prior to Release 9.4 and Cisco ASA Software Releases 9.5 and 9.7 have reached end of maintenance. Customers should migrate to a supported release that includes the fix for this vulnerability.

  Cisco FTD Software

  Cisco Firepower and FMC Software	Recommended Release for This Vulnerability	Recommended Release for All the Vulnerabilities Described in the Collection of Advisories
  6.0	6.2.3.12	6.2.3.12
  6.0.1	6.2.3.12	6.2.3.12
  6.1.0	6.2.3.12	6.2.3.12
  6.2.0	6.2.3.12	6.2.3.12
  6.2.1	6.2.3.12	6.2.3.12
  6.2.2	6.2.3.12	6.2.3.12
  6.2.3	6.2.3.12	6.2.3.12
  6.3.0	Not vulnerable	6.3.0.3
  6.4.0	Not vulnerable	Not vulnerable

  To upgrade to a fixed release of Cisco FTD Software, customers can do one of the following:

  • For devices that are managed by using Cisco Firepower Management Center (FMC), use the FMC interface to install the upgrade. After installation is complete, reapply the access control policy.
  • For devices that are managed by using Cisco Firepower Device Manager (FDM), use the FDM interface to install the upgrade. After installation is complete, reapply the access control policy.

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

• Cisco would like to thank Jason Moulder of Pratum for reporting this vulnerability.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190501-sd-cpu-dos

Revision History

• Version	Description	Section	Status	Date
  1.1	Updated the FTD fixed releases table to indicate that FTD Software Release 6.3.0.3 is available.	Fixed Software	Final	2019-May-02
  1.0	Initial public release.	—	Final	2019-May-01

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