Multiple Cisco Products Snort 3 Visual Basic for Applications Buffer Overflow Denial of Service Vulnerability

A vulnerability in the Snort 3 Visual Basic for Applications (VBA) Decompression Engine of multiple Cisco products could allow an unauthenticated, remote attacker to cause the Snort 3 Detection Engine to restart unexpectedly, resulting in a denial of service (DoS) condition. This vulnerability is due to improper range checking when Snort 3 decompresses VBA data, which is user controlled. An attacker could exploit this vulnerability by sending crafted VBA data to the Snort 3 Detection Engine of a targeted device. A successful exploit could allow the attacker to cause an overflow of stack data, which could result in a DoS condition. Cisco has released software updates that address this vulnerability. There is a workaround that addresses this vulnerability. This advisory is available at the following link: This advisory is part of a group of advisories. For a complete list of the advisories and links to them, see Cisco Advance Notification for Publication of October 21, 2026, Security Advisories . In addition, for further documentation of improvements and fixes in Open Source Snort 3, see Multiple Cisco Products Snort 3 Security Hardening Release: October 2026 .

A vulnerability in the Snort 3 Visual Basic for Applications (VBA) Decompression Engine of multiple Cisco products could allow an unauthenticated, remote attacker to cause the Snort 3 Detection Engine to restart unexpectedly, resulting in a denial of service (DoS) condition.

This vulnerability is due to improper range checking when Snort 3 decompresses VBA data, which is user controlled. An attacker could exploit this vulnerability by sending crafted VBA data to the Snort 3 Detection Engine of a targeted device. A successful exploit could allow the attacker to cause an overflow of stack data, which could result in a DoS condition.

Cisco has released software updates that address this vulnerability. There is a workaround that addresses this vulnerability.

This advisory is available at the following link:

This advisory is part of a group of advisories. For a complete list of the advisories and links to them, see Cisco Advance Notification for Publication of October 21, 2026, Security Advisories . In addition, for further documentation of improvements and fixes in Open Source Snort 3, see Multiple Cisco Products Snort 3 Security Hardening Release: October 2026 .

Vulnerable Products For information which products were affected by this vulnerability at the time of publication, see the following sections. Open Source Snort 3 At the time of publication, this vulnerability affected Open Source Snort 3. For information which Snort releases were vulnerable at the time of publication, see the Fixed Software section of this advisory. For more information on Snort, see the Snort website . Cisco Secure Firewall Threat Defense Software At the time of publication, this vulnerability affected Cisco Secure Firewall Threat Defense (FTD) Software if Snort 3 was configured and at least one Snort 3 Detector was configured for VBA macro decompression. Notes: VBA macro decompression is not enabled by default. The first Cisco Secure FTD Software release to support VBA decompression is Release 7.2.0. For more information, see the Firewall Management Center Features in Version 7.2.0 table in the Cisco Secure Firewall Threat Defense Release Notes . VBA macro decompression is supported for IMAP, SMTP, HTTP, and POP3 Snort Inspector Engines. For more information, see the Snort 3 Inspector Reference and the Custom Snort 3 Intrusion Policies for Access Control . For information which Cisco Secure FTD Software releases are vulnerable, see the Fixed Software section of this advisory. Determine the Snort Configuration on Cisco Secure FTD Software On new installations of Cisco Secure FTD Software releases 7.0.0 and later, Snort 3 is running by default. On devices that were running Cisco Secure FTD Software Release 6.7.0 or earlier and were upgraded to Release 7.0.0 or later, Snort 2 is running by default. Snort 2 was deprecated in Cisco Secure FTD Software releases 7.7.0 and later. To determine if Snort 3 is running on Cisco Secure FTD Software, see Determine the Active Snort Version that Runs on FTD . Snort 3 must be active for this vulnerability to be exploited. Unified Threat Defense on Cisco IOS XE Software At the time of publication, this vulnerability affected the following Cisco products if they were running a vulnerable release of Unified Threat Defense (UTD) Snort IPS Engine for Cisco IOS XE Software or UTD Engine for Cisco IOS XE SD-WAN Software: 1000 Series Integrated Services Routers (ISRs) 4000 Series ISRs 8100 Series Secure Routers 8200 Series Secure Routers 8300 Series Secure Routers 8400 Series Secure Routers Catalyst 8000V Edge Software Catalyst 8200 Series Edge Platforms Catalyst 8300 Series Edge Platforms Catalyst 8500L Edge Platforms Catalyst IR1800 Rugged Series Routers Catalyst IR8340 Rugged Routers Cloud Services Routers 1000V Integrated Services Virtual Routers Note: UTD is not installed on these devices by default. If the UTD file is not installed, the device is not affected by this vulnerability. For information which Cisco IOS XE Software releases were vulnerable at the time of publication, see the Fixed Software section of this advisory. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information. Determine Whether UTD Is Enabled To determine whether UTD is enabled on a device, use the show utd engine standard status command. If the output shows a Yes under Running , UTD is enabled. If there is no output, the device is not affected. The following example shows the output on a device that has UTD enabled: Router# show utd engine standard status Engine version : 1.0.19_SV2.9.16.1_XE17.3 Profile : Cloud-Low System memory : Usage : 6.00 % Status : Green Number of engines : 1 Engine Running Health Reason =========================================== Engine(#1): Yes Green None ======================================================= . . . 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 Cloud-delivered Firewall (CDFW) Cisco Cyber Vision Cisco Meraki products Cisco Secure Access (CSA) Cisco Secure Firewall Adaptive Security Appliance (ASA) Software Cisco Secure Firewall Management Center (FMC) Software Open Source Snort 2 Note: Open Source Snort 2 has reached End of Life. For more information, see End of Life Announcement for Open Source Snort 2 .

For information which products were affected by this vulnerability at the time of publication, see the following sections.

At the time of publication, this vulnerability affected Open Source Snort 3.

For information which Snort releases were vulnerable at the time of publication, see the Fixed Software section of this advisory. For more information on Snort, see the Snort website .

Cisco Secure Firewall Threat Defense Software

At the time of publication, this vulnerability affected Cisco Secure Firewall Threat Defense (FTD) Software if Snort 3 was configured and at least one Snort 3 Detector was configured for VBA macro decompression.

VBA macro decompression is not enabled by default.

The first Cisco Secure FTD Software release to support VBA decompression is Release 7.2.0. For more information, see the Firewall Management Center Features in Version 7.2.0 table in the Cisco Secure Firewall Threat Defense Release Notes .

VBA macro decompression is supported for IMAP, SMTP, HTTP, and POP3 Snort Inspector Engines. For more information, see the Snort 3 Inspector Reference and the Custom Snort 3 Intrusion Policies for Access Control .

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

Determine the Snort Configuration on Cisco Secure FTD Software

On new installations of Cisco Secure FTD Software releases 7.0.0 and later, Snort 3 is running by default. On devices that were running Cisco Secure FTD Software Release 6.7.0 or earlier and were upgraded to Release 7.0.0 or later, Snort 2 is running by default.

Snort 2 was deprecated in Cisco Secure FTD Software releases 7.7.0 and later.

To determine if Snort 3 is running on Cisco Secure FTD Software, see Determine the Active Snort Version that Runs on FTD . Snort 3 must be active for this vulnerability to be exploited.

Unified Threat Defense on Cisco IOS XE Software

At the time of publication, this vulnerability affected the following Cisco products if they were running a vulnerable release of Unified Threat Defense (UTD) Snort IPS Engine for Cisco IOS XE Software or UTD Engine for Cisco IOS XE SD-WAN Software:

1000 Series Integrated Services Routers (ISRs)

8100 Series Secure Routers

8200 Series Secure Routers

8300 Series Secure Routers

8400 Series Secure Routers

Catalyst 8000V Edge Software

Catalyst 8200 Series Edge Platforms

Catalyst 8300 Series Edge Platforms

Catalyst 8500L Edge Platforms

Catalyst IR1800 Rugged Series Routers

Catalyst IR8340 Rugged Routers

Cloud Services Routers 1000V

Integrated Services Virtual Routers

Note: UTD is not installed on these devices by default. If the UTD file is not installed, the device is not affected by this vulnerability.

For information which Cisco IOS XE Software releases were vulnerable at the time of publication, see the Fixed Software section of this advisory. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.

Determine Whether UTD Is Enabled

To determine whether UTD is enabled on a device, use the show utd engine standard status command. If the output shows a Yes under Running , UTD is enabled. If there is no output, the device is not affected. The following example shows the output on a device that has UTD enabled:

Router# show utd engine standard status Engine version : 1.0.19_SV2.9.16.1_XE17.3 Profile : Cloud-Low System memory : Usage : 6.00 % Status : Green Number of engines : 1 Engine Running Health Reason =========================================== Engine(#1): Yes Green None ======================================================= . . .

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 Cloud-delivered Firewall (CDFW)

Cisco Meraki products

Cisco Secure Access (CSA)

Cisco Secure Firewall Adaptive Security Appliance (ASA) Software

Cisco Secure Firewall Management Center (FMC) Software

Note: Open Source Snort 2 has reached End of Life. For more information, see End of Life Announcement for Open Source Snort 2 .

There is a workaround that addresses this vulnerability. This vulnerability is due to VBA decompression, which is not enabled by default for any Snort 3 Inspector. If VBA decompression is disabled until the device can be upgraded to a fixed software release, the device will not be affected by this vulnerability. For more details on how to remove the VBA configuration, see the following references: Firewall Management Center Features in Version 7.2.0 Snort 3 Inspector Reference Custom Snort 3 Intrusion Policies for Access Control 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.

There is a workaround that addresses this vulnerability.

This vulnerability is due to VBA decompression, which is not enabled by default for any Snort 3 Inspector. If VBA decompression is disabled until the device can be upgraded to a fixed software release, the device will not be affected by this vulnerability. For more details on how to remove the VBA configuration, see the following references:

Firewall Management Center Features in Version 7.2.0

Snort 3 Inspector Reference

Custom Snort 3 Intrusion Policies for Access Control

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.

Cisco considers any workarounds and mitigations (if applicable) to be temporary solutions until an upgrade to a fixed software release is available. To 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. Fixed Releases The Cisco Product Security Incident Response Team (PSIRT) validates only the affected and fixed release information that is documented in this advisory. For information fixed releases, see the following sections. Open Source Snort Software At the time of publication, the release information in the following table was accurate. The left column lists Snort software releases, and the right column indicates whether a release was affected by the vulnerability that is described in this advisory and which release included the fix for this vulnerability. Snort 3 Release First Fixed Release 3.x 3.12.4.0 Note: This fix is also included as part of the broader hardening improvements that are disclosed in the security advisory Multiple Cisco Products Snort 3 Security Hardening Release: October 2026 . 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 for vulnerabilities that affect a specific software release. To use the form, follow these steps: Choose which advisories the tool will -all advisories, only advisories with a Critical or High Security Impact Rating (SIR) , or only this advisory. Choose the appropriate software. Choose the appropriate platform. 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. Click Check . 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 UTD on Cisco IOS XE Software At the time of publication, the release information in the following table was accurate. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information. In the following table, the left column lists Cisco IOS XE Software releases, and the right column indicates whether a release was affected by the vulnerability that is described in this advisory and which release included the fix for this vulnerability. Cisco IOS XE Software Release First Fixed Release 17.12 17.12.8 17.15 17.15.6 17.18 17.18.5 26.1 26.1.2 26.2 26.2.1

Cisco considers any workarounds and mitigations (if applicable) to be temporary solutions until an upgrade to a fixed software release is available. To 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.

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

For information fixed releases, see the following sections.

Open Source Snort Software

At the time of publication, the release information in the following table was accurate.

The left column lists Snort software releases, and the right column indicates whether a release was affected by the vulnerability that is described in this advisory and which release included the fix for this vulnerability.

Note: This fix is also included as part of the broader hardening improvements that are disclosed in the security advisory Multiple Cisco Products Snort 3 Security Hardening Release: October 2026 .

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 for vulnerabilities that affect a specific software release. To use the form, follow these steps:

Choose which advisories the tool will -all advisories, only advisories with a Critical or High Security Impact Rating (SIR) , or only this advisory.

Choose the appropriate software.

Choose the appropriate platform.

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.

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

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

UTD on Cisco IOS XE Software

At the time of publication, the release information in the following table was accurate. See the Details section in the bug ID(s) at the top of this advisory for the most complete and current information.

In the following table, the left column lists Cisco IOS XE Software releases, and the right column indicates whether a release was affected by the vulnerability that is described in this advisory and which release included the fix for this vulnerability.

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.

The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.

Cisco would like to thank the following people for reporting this vulnerability: Alessandro Greco, an independent security researcher Guillermo Muñoz Mozos, an independent security researcher TristanInSec, working with TrendAI Zero Day Initiative Yazan Balawneh of CyStack.ps Yazdan Soltani

Cisco would like to thank the following people for reporting this vulnerability:

Alessandro Greco, an independent security researcher

Guillermo Muñoz Mozos, an independent security researcher

TristanInSec, working with TrendAI Zero Day Initiative

Yazan Balawneh of CyStack.ps

Cisco Security Vulnerability Policy

To learn Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy . This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco. For additional information on Cisco's vulnerability management, disclosure cadence, and software patching strategy, see Cisco's Transition to a Risk-Based Vulnerability Disclosure Model .

To learn Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy . This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.

For additional information on Cisco's vulnerability management, disclosure cadence, and software patching strategy, see Cisco's Transition to a Risk-Based Vulnerability Disclosure Model .

Related to This Advisory

Version Description Section Status Date 1.0 Initial public release. - Final 2026-OCT-21 Show Less

SOFTWARE DOWNLOADS AND TECHNICAL SUPPORT The Cisco Support and Downloads page on Cisco.com provides information licensing and downloads. This page can also display customer device support coverage for customers who use the My Devices tool. Please note that customers may download only software that was procured from Cisco directly or through a Cisco authorized reseller or partner and for which the license is still valid. 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 Technical Assistance Center (TAC) . 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. When considering software upgrades , customers are advised to regularly consult the advisories for the relevant Cisco products 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 the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers. LEGAL DISCLAIMER DETAILS CISCO DOES NOT MAKE ANY EXPRESS OR IMPLIED GUARANTEES OR WARRANTIES OF ANY KIND, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. WITHOUT LIMITING THE GENERALITY OF THE FOREGOING, CISCO DOES NOT GUARANTEE THE ACCURACY OR COMPLETENESS OF THIS INFORMATION. THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME. Copies or summaries of the information contained in this Security Advisory may lack important information or contain factual errors. Customers are advised to visit the Cisco Security Advisories page for the most recent version of this Security Advisory. The Cisco Product Security Incident Response Team (PSIRT) assesses only the affected and fixed release information that is documented in this advisory. See the Cisco Security Vulnerability Policy for more information.

SOFTWARE DOWNLOADS AND TECHNICAL SUPPORT

The Cisco Support and Downloads page on Cisco.com provides information licensing and downloads. This page can also display customer device support coverage for customers who use the My Devices tool. Please note that customers may download only software that was procured from Cisco directly or through a Cisco authorized reseller or partner and for which the license is still valid.

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 Technical Assistance Center (TAC) . 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.

When considering software upgrades , customers are advised to regularly consult the advisories for the relevant Cisco products 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 the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.

LEGAL DISCLAIMER DETAILS

CISCO DOES NOT MAKE ANY EXPRESS OR IMPLIED GUARANTEES OR WARRANTIES OF ANY KIND, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. WITHOUT LIMITING THE GENERALITY OF THE FOREGOING, CISCO DOES NOT GUARANTEE THE ACCURACY OR COMPLETENESS OF THIS INFORMATION. THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.

Copies or summaries of the information contained in this Security Advisory may lack important information or contain factual errors. Customers are advised to visit the Cisco Security Advisories page for the most recent version of this Security Advisory. The Cisco Product Security Incident Response Team (PSIRT) assesses only the affected and fixed release information that is documented in this advisory. See the Cisco Security Vulnerability Policy for more information.

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