Summary

• A vulnerability in the remote access VPN session manager of Cisco Adaptive Security Appliance (ASA) Software could allow a unauthenticated, remote attacker to cause a denial of service (DoS) condition on the remote access VPN services.

  The vulnerability is due to an issue with the remote access VPN session manager. An attacker could exploit this vulnerability by requesting an excessive number of remote access VPN sessions. An exploit could allow the attacker to cause a DoS condition.

  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-20190501-asa-vpn-dos

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco ASA Software. For information about affected software releases, consult the tables in the Fixed Software section of this advisory.

  The following Cisco products are affected by this vulnerability if configured for multi-context:

  • 3000 Series Industrial Security Appliances (ISA)
  • ASA 5500-X Series Firewalls
  • ASA Services Module for Cisco Catalyst 6500 Series Switches and Cisco 7600 Series Routers
  • Firepower 2100 Series
  • Firepower 4100 Series
  • Firepower 9300 Security Appliances

  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 ASA Configuration

  To determine whether the ASA is configured in multi-context mode, administrators can use the show context command. The following display is sample output from the show context command, and shows three contexts:

  hostname# show context

  Context Name      Interfaces                    URL
  

  *admin            GigabitEthernet0/1.100        disk0:/admin.cfg
  

                    GigabitEthernet0/1.101
  

  contexta          GigabitEthernet0/1.200        disk0:/contexta.cfg
  

                    GigabitEthernet0/1.201
  

  contextb          GigabitEthernet0/1.300        disk0:/contextb.cfg
  

                    GigabitEthernet0/1.301
  

  Total active Security Contexts: 3
  

  To determine whether the ASA is configured for remote-access VPN, administrators can use the show running-config command and check for the commands tunnel-group <tunnel_group_name> type remote-access.

  Products Confirmed Not Vulnerable

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

Details

• The condition is triggered when users are challenged for a PIN or new password after the initial username/password authentication and the user fails to provide this information within five minutes. During this time, the ASA allocates a temporary license from a pool defined by the platform. When the time out expires, the ASA fails to delete the session’s temporary license. When all temporary licenses have been allocated, no additional connections are allowed.

Workarounds

• Customers can use the following command on the affected device to temporarily clear the condition or reboot the device:

  vpn-sessiondb logoff all

Fixed Software

• Cisco has released free software updates that address the vulnerabilities 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. In the following table(s), the left column lists Cisco software releases. The right column indicates whether a release is affected by the vulnerability described in this advisory and the release that includes the fix for this vulnerability.

  Cisco ASA Software

  Cisco ASA Software Release	Recommended Release for This Vulnerability
  Prior to 9.41	Not vulnerable
  9.4	9.4.4.34
  9.51	9.6.4.25
  9.6	9.6.4.25
  9.71	9.8.4
  9.8	9.8.4
  9.9	9.9.2.50
  9.10	9.10.1.17
  9.12	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.

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://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20190501-asa-vpn-dos

Revision History

• Version	Description	Section	Status	Date
  1.1	Removed reference to Firepower Threat Defense Software in Determining the Cisco FTD Software Release and Fixed Releases.	Determining the Cisco FTD Software Release and Fixed Releases	Final	2019-May-01
  1.0	Initial public release.	—	Final	2019-May-01

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