Summary

• A vulnerability in the Snort 2 and Snort 3 deep packet inspection of Cisco Secure Firewall Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to bypass configured Snort rules and allow traffic onto the network that should have been dropped.

  This vulnerability is due to a logic error in the integration of the Snort Engine rules with Cisco Secure FTD Software that could allow different Snort rules to be hit when deep inspection of the packet is performed for the inner and outer connections. An attacker could exploit this vulnerability by sending crafted traffic to a targeted device that would hit configured Snort rules. A successful exploit could allow the attacker to send traffic to a network where it should have been denied.

  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-snort-bypass-rLggKzVF

  This advisory is part of the March 2026 release of the Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software Security Advisory Bundled Publication. For a complete list of the advisories and links to them, see Cisco Event Response: March 2026 Semiannual Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software Security Advisory Bundled Publication.

Affected Products

• Vulnerable Products

  At the time of publication, this vulnerability affected Cisco devices if they were running a vulnerable release of Cisco Secure FTD Software and had an intrusion policy enabled that had a Snort Detection Engine running.

  This vulnerability also affected Cisco products if they were running a vulnerable release of Cisco Secure FTD Software and had Snort 2 or Snort 3 enabled.

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

  Determine the Snort Configuration on Cisco Secure FTD Software

  To determine if Snort 2 or Snort 3 is running on Cisco Secure FTD Software, see Determine the Active Snort Version that Runs on Firepower Threat Defense (FTD).

  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 Secure Firewall Adaptive Security Appliance (ASA) Software
  • Cisco Secure Firewall Management Center (FMC) Software
  • Cisco Cyber Vision
  • Cisco Meraki products
  • Cisco Secure Access - Secure Internet Access (SIA) Advantage
  • Cisco Secure Access - Secure Private Access (SPA) Advantage
  • Cisco Umbrella Cloud-delivered Firewall (CDFW), formerly Umbrella Secure Internet Gateway (SIG)
  • Cisco Unified Threat Defense (UTD)
  • Open Source Snort 2
  • Open Source Snort 3

Workarounds

• There are no workarounds that address this vulnerability.

Fixed Software

• Cisco considers any workarounds and mitigations (if applicable) to be temporary solutions until an upgrade to a fixed software release is available. To fully remediate this vulnerability and avoid future exposure as described in this advisory, Cisco strongly recommends that customers upgrade to the fixed software indicated in this advisory.

  Cisco Secure Firewall ASA, Secure FMC, and Secure FTD Software

  To help customers determine their exposure to vulnerabilities in Cisco Secure Firewall ASA, Secure FMC, and Secure 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, 9.20.3.4 for Cisco Secure Firewall ASA Software or 7.4.2 for Cisco Secure 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 1200 Series Secure Firewall 3100 Series Secure Firewall 4200 Series

   

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

  Additional Resources

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

  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 Technical Assistance Center (TAC) support case.

URL

• https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-snort-bypass-rLggKzVF

Revision History

• Version	Description	Section	Status	Date
  1.0	Initial public release.	—	Final	2026-MAR-04

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