Summary

• A vulnerability in the SIP inspection engine of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a crash and reload of an affected device, resulting in a denial of service (DoS) condition.
  
  The vulnerability is due to a crash that occurs during a hash lookup for a SIP pinhole connection. An attacker could exploit this vulnerability by sending crafted SIP traffic through an affected device. A successful exploit could allow the attacker to cause a crash and reload of the 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://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asa-ftd-sipdos-GGwmMerC

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

Affected Products

• Vulnerable Products

  This vulnerability affects Cisco products if they are running a vulnerable release of Cisco ASA Software or FTD Software and have SIP inspection configured.

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

  Determine the Device Configuration

  To determine if SIP inspection is configured on Cisco ASA Software or FTD Software, use the show service-policy | include sip command at the CLI. The device is considered vulnerable if the output includes Inspect: sip, as shown in this example:

  device# show service-policy | include sip
  Inspect: sip , packet 2, lock fail 0, drop 0, reset-drop 0, 5-min-pkt-rate 0 pkts/sec, v6-fail-close 0 sctp-drop-override 0 

  Note: SIP inspection is enabled by default on Cisco ASA Software and FTD Software. For detailed information about the default settings for application inspection policies, see the Cisco ASA Series Firewall CLI Configuration Guide.

  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 Firepower Management Center (FMC) Software.

Workarounds

• There are no workarounds that address this vulnerability. However, there are mitigation options that apply to both physical and virtual appliances.

  Option 1: Disable SIP Inspection

  Disabling SIP inspection will completely close the attack vector for this vulnerability. However, this mitigation may not be suitable for all customers. In particular, disabling SIP inspection would break SIP connections if either Network Address Translation (NAT) is applied to SIP traffic or if any ports that are required for SIP communication are not opened through ACL.

  To disable SIP inspection in Cisco ASA Software, use the following command:

  policy-map 
   class inspection_default
    no inspect sip

  To disable SIP inspection in Cisco FTD Software, use the following command in the CLI:

  configure inspection sip disable
  

  
  

  Option 2: Allow Only Trusted SIP Hosts Using ACLs

  Use ACLs to limit SIP connection through the device to known, trusted SIP hosts. For information on Cisco ASA and FTD ACL configuration, see Cisco ASA Series Firewall CLI Configuration Guide: Access Control Lists.

  While these mitigations have been deployed and were 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 vulnerabilities described in this bundle and which release includes fixes for those vulnerabilities.

  ASA Software

  Cisco ASA Software Release	First Fixed Release for This Vulnerability	First Fixed Release for All the Vulnerabilities Described in the Bundle of Advisories
  Earlier than 9.81	Not vulnerable.	Migrate to a fixed release.
  9.8	9.8.4.34	9.8.4.35
  9.9	9.9.2.85	9.9.2.85
  9.101	Migrate to a fixed release.	Migrate to a fixed release.
  9.12	9.12.4.18	9.12.4.18
  9.13	9.13.1.21	9.13.1.21
  9.14	9.14.2.13	9.14.2.13
  9.15	9.15.1.15	9.15.1.15

  1. Cisco ASA Software releases 9.7 and earlier, as well as Release 9.10, have reached end of software maintenance. Customers are advised to migrate to a supported release that includes the fix for this vulnerability.

  FTD Software

  Cisco FTD Software Release	First Fixed Release for This Vulnerability	Recommended Release for All the Vulnerabilities Described in the Bundle of Advisories
  Earlier than 6.2.21	Not vulnerable.	Migrate to a fixed release.
  6.2.2	Migrate to a fixed release.	Migrate to a fixed release.
  6.2.3	Migrate to a fixed release.	Migrate to a fixed release.
  6.3.0	Migrate to a fixed release.	Migrate to a fixed release.
  6.4.0	6.4.0.12 (May 2021)	6.4.0.12 (May 2021)
  6.5.0	Migrate to a fixed release.	Migrate to a fixed release.
  6.6.0	6.6.4	6.6.42
  6.7.0	6.7.0.2	6.7.0.2

  1. Cisco FMC and FTD Software releases 6.0.1 and earlier, as well as releases 6.2.0 and 6.2.1, have reached end of software maintenance. Customers are advised to migrate to a supported release that includes the fix for this vulnerability.

  2. The First Fixed Release for the 6.6.0 code train was 6.6.3; however, due to upgrade issues associated with CSCvx86231 the recommended release is 6.6.4.

  To upgrade to a fixed release of Cisco FTD Software, 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

• 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-asa-ftd-sipdos-GGwmMerC

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2021-APR-28

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