Summary

• A vulnerability in the processing of SSH connections for multi-instance deployments of Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on the affected device.

  This vulnerability is due to a lack of proper error handling when an SSH session fails to be established. An attacker could exploit this vulnerability by sending a high rate of crafted SSH connections to the instance. A successful exploit could allow the attacker to cause resource exhaustion, which causes a DoS condition on the affected device. The device must be manually reloaded to recover.

  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-ftd-dos-rUDseW3r

  This advisory is part of the October 2021 release of the Cisco ASA, FTD, and FMC Security Advisory Bundled publication. For a complete list of the advisories and links to them, see Cisco Event Response: October 2021 Cisco ASA, FMC, and FTD Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  This vulnerability affects devices if they are running a vulnerable release of Cisco FTD Software that is configured for multi-instance operation. Multi-instance configuration support was introduced in Cisco FTD Software Release 6.3.0; earlier releases are not affected by this multi-instance vulnerability.

  The only Cisco FTD Software platforms that support multi-instance operation are the following:

  • Firepower 4100 Series Security Appliances
  • Firepower 9300 Series Security Appliances

  Note: Affected devices are vulnerable only when accessed from an IP address in the configured SSH command range. The SSH service is enabled by default on all devices that run Cisco FTD Software.

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

  Determine the Device Configuration
  

  To determine whether a device is providing multi-instance services, log in to the Cisco FXOS CLI and use the show app-instance command within the ssa scope. If the Deploy Type field has a value of Container, application instances are present and the device is vulnerable. The following example shows the command output for a vulnerable device:

  firepower# scope ssa
  firepower /ssa # show app-instance
  
  

  App Name	Identifier	Slot ID	Admin State	Oper State	Running Version	Startup Version	Deploy Type	Turbo Mode	Profile Name	Cluster State	Cluster Role
  -----	-------	------	------	-----	-------	-------	------	-----	-----	-------	-------
  ftd	ftd1	1	Enabled	Online	6.2.3.14	6.2.3.14	Native	No		Not Applicable	None
  ftd	ftd2-1	2	Enabled	Online	6.4.0.4	6.4.0.4	Container	No	mid	Not Applicable

  
  

  Products Confirmed Not Vulnerable

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

  Cisco has confirmed that this vulnerability does not affect Cisco Adaptive Security Appliance (ASA) Software or Cisco Firepower Management Center (FMC) Software.

Workarounds

• There are no workarounds that address this vulnerability.

  However, as a mitigation, administrators can allow only trusted networks and hosts to have SSH access to the FTD management IP. This will limit the attack surface of this vulnerability. See Harden FTD User Access for more information.

  While this mitigation has been deployed and was proven successful in a test environment, customers should determine the applicability and effectiveness in their own environment and under their own use conditions. Customers should be aware that any workaround or mitigation that is implemented may negatively impact the functionality or performance of their network based on intrinsic customer deployment scenarios and limitations. Customers should not deploy any workarounds or mitigations before first evaluating the applicability to their own environment and any impact to such environment.

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 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

  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 first release that includes the fix for this vulnerability. The right column indicates whether a release is affected by any of the Critical or High SIR vulnerabilities described in this bundle and which release includes fixes for those vulnerabilities.

  FTD Software

  Cisco FTD Release	First Fixed Release for This Vulnerability	First Fixed Release for All Vulnerabilities Described in the Bundle of Advisories
  6.2.2 and earlier 1	Not vulnerable.	Migrate to a fixed release.
  6.2.3	Not vulnerable.	Migrate to a fixed release.
  6.3.0 1	Migrate to a fixed release.	Migrate to a fixed release.
  6.4.0	6.4.0.13 (Nov 2021)	6.4.0.13 (Nov 2021)
  6.5.0 1	Migrate to a fixed release.	Migrate to a fixed release.
  6.6.0	6.6.5	6.6.5.1 (Nov 2021)
  6.7.0	6.7.0.3 (Jan 2022)	6.7.0.3 (Jan 2022)
  7.0.0	7.0.1	7.0.1

  1. Cisco FMC and FTD Software releases 6.2.2 and earlier, as well as releases 6.3.0 and 6.5.0, have reached end of software maintenance. Customers are advised to migrate to a supported release that includes the fix for this vulnerability.

  For instructions on upgrading your FTD device, see Cisco Firepower Management Center Upgrade Guide.

  The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory.

Exploitation and Public Announcements

• The Cisco 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-ftd-dos-rUDseW3r

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2021-OCT-27

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