Multiple Cisco Products Snort 3 SMTP MIME Denial of Service Vulnerability

Multiple Cisco products are affected by a vulnerability in the Snort 3 SMTP MIME Decoder that could allow an unauthenticated, remote attacker to cause the Snort 3 Detection Engine to restart. This vulnerability is due to a lack of error checking when the MIME fields of the SMTP header are parsed. An attacker could exploit this vulnerability by sending crafted SMTP packets through an established connection to be parsed by Snort 3. A successful exploit could allow the attacker to cause a denial of service (DoS) condition when the Snort 3 Detection Engine unexpectedly restarts. 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: 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 Snort 3, see Multiple Cisco Products Snort 3 Security Hardening Release: October 2026 .

Multiple Cisco products are affected by a vulnerability in the Snort 3 SMTP MIME Decoder that could allow an unauthenticated, remote attacker to cause the Snort 3 Detection Engine to restart.

This vulnerability is due to a lack of error checking when the MIME fields of the SMTP header are parsed. An attacker could exploit this vulnerability by sending crafted SMTP packets through an established connection to be parsed by Snort 3. A successful exploit could allow the attacker to cause a denial of service (DoS) condition when the Snort 3 Detection Engine unexpectedly restarts.

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:

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 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. 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 Firepower Threat Defense (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 ======================================================= . . . Cisco Meraki MX Security Appliances At the time of publication, this vulnerability affected the following products if they were running a vulnerable release of Cisco Meraki software: MX64 MX64W MX65 MX65W MX67 MX67C MX67W MX68 MX68CW MX75 MX84 MX85 MX95 MX100 MX105 MX250 MX400 MX450 MX600 For details automatic upgrades of devices that are connected to the Cisco Meraki Dashboard, see the Fixed Software section of this advisory. 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 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.

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 Firepower Threat Defense (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 ======================================================= . . .

Cisco Meraki MX Security Appliances

At the time of publication, this vulnerability affected the following products if they were running a vulnerable release of Cisco Meraki software:

For details automatic upgrades of devices that are connected to the Cisco Meraki Dashboard, see the Fixed Software section of this advisory.

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 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 are no workarounds that address this vulnerability.

There are no workarounds that address this vulnerability.

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 3 At the time of publication, the release information in the following table was accurate. The left column lists Snort 3 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 3.10.1.0 3.12.4.0* *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: CSCwt04581 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 Meraki MX Security Appliances Snort is integrated natively into Cisco Meraki security appliances as part of the threat protection services that are managed automatically through the Meraki Dashboard. No customer action is required to download Meraki firmware or the Snort 3 package for Meraki devices. As of October 21, 2026, all Meraki models listed in this advisory that are online and connected to the Cisco Meraki Dashboard have been automatically updated with the Snort 3 package.

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.

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

The left column lists Snort 3 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 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: CSCwt04581

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 Meraki MX Security Appliances

Snort is integrated natively into Cisco Meraki security appliances as part of the threat protection services that are managed automatically through the Meraki Dashboard. No customer action is required to download Meraki firmware or the Snort 3 package for Meraki devices. As of October 21, 2026, all Meraki models listed in this advisory that are online and connected to the Cisco Meraki Dashboard have been automatically updated with the Snort 3 package.

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.

This vulnerability was found during the resolution of a Cisco Technical Assistance Center (TAC) support case.

This vulnerability was found during the resolution of a Cisco Technical Assistance Center (TAC) support case.

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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