Summary

• A vulnerability in the interaction between the TCP Intercept feature and the Snort 3 detection engine on Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to bypass configured policies on an affected system. Devices that are configured with Snort 2 are not affected by this vulnerability.

  This vulnerability is due to a logic error when handling embryonic (half-open) TCP connections. An attacker could exploit this vulnerability by sending a crafted traffic pattern through an affected device. A successful exploit could allow unintended traffic to enter the network protected by the 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-snort-bypass-PTry37fX

  This advisory is part of the October 2024 release of the 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: October 2024 Semiannual Cisco ASA, FMC, and FTD Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  At the time of publication, this vulnerability affected Cisco FTD Software and Cisco FirePOWER Services if they were configured with a maximum embryonic connection using the Snort 3 detection engine.

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

  Determine the Snort Configuration on Cisco FTD Software

  To determine if Snort 3 is running on Cisco FTD Software, see Determine the Active Snort Version that Runs on Firepower Threat Defense (FTD). Snort 3 has to be active for this vulnerability to be exploited.

  Determine the Embryonic Configuration on Cisco FTD Software

  The default value for embryonic connections is 0, which is unlimited connections. Deployments with the default configuration are considered not vulnerable.

  To determine the embryonic connection configuration, use the show running-config policy-map | include embryonic FTD CLI command. The following example shows the output of the command on a device that has a maximum embryonic connection set:

  FTD# show running-config policy-map | include embryonic
    set connection conn-max 1000 embryonic-conn-max 3000
  FTD#

  If the command shows no output, the device is considered not vulnerable.

  For more information on embryonic connections, see the Protect Servers from a SYN Flood DoS Attack (TCP Intercept) section or the What Are Connection Settings? section of of the Cisco Secure Firewall Management Center Device 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 the following products:

  • Cisco Adaptive Security Appliance (ASA) Software
  • Cisco Secure Firewall Management Center (FMC) Software, formerly Firepower Management Center Software
  • Open Source Snort 2
  • Open Source Snort 3

Workarounds

• There is a workaround that addresses this vulnerability. To implement the workaround, turn off pkt-decode-optimization using the no asp inspect-dp pkt-decode-optimization FTD CLI command, as shown in the following example:

  FTD# no asp inspect-dp pkt-decode-optimization
  FTD#

  While this workaround 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

• 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.

  Cisco ASA, FMC, and FTD Software

  To help customers determine their exposure to vulnerabilities in Cisco ASA, FMC, and FTD Software, Cisco provides the Cisco Software Checker. This tool identifies any Cisco security advisories that impact a specific software release and the earliest release that fixes the vulnerabilities that are described in each advisory (“First Fixed”). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities that are described in all the advisories that the Software Checker identifies (“Combined First Fixed”).

  To use the tool, go to the Cisco Software Checker page and follow the instructions. Alternatively, use the following form to search for vulnerabilities that affect a specific software release. To use the form, follow these steps:

  1. Choose which advisories the tool will search-all advisories, only advisories with a Critical or High Security Impact Rating (SIR), or only this advisory.
  2. Choose the appropriate software.
  3. Choose the appropriate platform.
  4. Enter a release number-for example, 9.16.2.11 for Cisco ASA Software or 6.6.7 for Cisco FTD Software.
  5. Click Check.

  Only this advisory All Critical and High advisories All advisories Cisco ASA Software Cisco FMC Software Cisco FTD Software Any Platform 3000 Series Industrial Security Appliances (ISA) ASA 5500-X Series Firewalls ASA Service Module Adaptive Security Virtual Appliance (ASAv) Firepower 1000 Series Firepower 2100 Series Firepower 4100 Series Firepower 9000 Series Secure Firewall 3100 Series

  
  

  For instructions on upgrading a Cisco FTD device, see the appropriate Cisco FMC upgrade guide.

  
  

  Additional Resources

  For help determining the best Cisco ASA, FMC, or FTD Software release, see the following Recommended Releases documents. If a security advisory recommends a later release, Cisco recommends following the advisory guidance.

  Cisco ASA Compatibility
  Cisco Secure Firewall ASA Upgrade Guide
  Cisco Secure Firewall Threat Defense Compatibility Guide

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-snort-bypass-PTry37fX

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	-	Final	2024-OCT-23

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