Cisco Security Advisory
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CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H/E:X/RL:X/RC:X
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As part of Cisco's ongoing commitment to proactive security and product quality, the Cisco owned Open Source Snort 3 Software engineering team has conducted a comprehensive internal security review. This review resulted in software hardening releases that address multiple internally discovered vulnerabilities.
The vulnerabilities tracked by CVE-2026-20043 are related to issues concerning out-of-bounds writes that are grouped under the Common Weakness Enumeration (CWE) Base CWE-787.
As part of Cisco's ongoing commitment to proactive security and product quality, the Cisco-owned Open Source Snort 3 engineering team has conducted a comprehensive internal security review. This review resulted in software hardening releases that address multiple internally discovered vulnerabilities.
These vulnerabilities were found during internal testing and are not known to be actively exploited. To assist customers in patching and to streamline the disclosure process, Cisco has grouped these issues by their underlying vulnerability class - Common Weakness Enumeration (CWE) - and assigned a single Common Vulnerabilities and Exposures Identifier (CVE ID) to each CWE grouping.
Note: Cisco may publish separate security advisories that provide additional details about individual vulnerabilities that are addressed in this release.
Cisco has released software updates that address these vulnerabilities. There are no workarounds that address these vulnerabilities.
This advisory is available at the following link:
https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-hardening-snort3-ybgmhTQeThis 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.
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Vulnerable Products
These vulnerabilities affect the following products, regardless of device configuration:
- Cisco Cloud-delivered Firewall (CDFW)
- Cisco Cyber Vision
- Cisco Meraki MX Security Appliances
- Cisco Secure Access (CSA)
- Cisco Secure Firewall Threat Defense (FTD) Software
- Open Source Snort 3
- Unified Threat Defense (UTD) on Cisco IOS XE Software
For information about which Cisco software releases are vulnerable, 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 these vulnerabilities.
Cisco has confirmed that these vulnerabilities do not affect 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.
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The following table outlines the vulnerability classes that are addressed in this hardening release. The CVSS score that is assigned to each CVE ID represents the maximum potential severity of the single most impactful underlying vulnerability within that specific CWE category.
CVE ID Highest CVSS Score Vulnerability Class (Highest-Level CWE) Description CVE-2026-20236 9.0 CWE-682 Incorrect calculation CVE-2026-20043 9.0 CWE-787 Out-of-bounds write CVE-2026-20291 7.8 CWE-269 Improper privilege management CVE-2026-20356 7.5 CWE-400 Uncontrolled resource consumption
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There are no workarounds that address these vulnerabilities.
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To remediate these vulnerabilities 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 about fixed releases, see the following sections.
Open Source Snort 3
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 Cyber Vision
In the following table, the left column lists Cisco software releases. The right column indicates whether a release is affected by the vulnerabilities that are described in this advisory and the first release that includes the fix for these vulnerabilities. Customers are advised to upgrade to an appropriate fixed software release as indicated in this section.
Cisco Cyber Vision Release First Fixed Release Earlier than 5.6 Migrate to a fixed release. 5.6 5.6.0 CDFW and CSA
Snort 3 is integrated natively into Cisco CDFW and CSA as part of the Snort 3 intrusion prevention system (IPS) technology to inspect traffic and block threats. No customer action is required. As of October 21, 2026, all Cisco CDFW and CSA cloud instances have been automatically updated with the Snort 3 package.
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.
Secure FTD Software
In the following table, the left column lists Cisco software releases. The right column indicates whether a release is affected by the vulnerabilities that are described in this advisory and the first release that includes the fix for these vulnerabilities. Customers are advised to upgrade to an appropriate fixed software release as indicated in this section.
Cisco Secure FTD Software Release First Fixed Release 7.0 and earlier 7.0.10 7.2 7.2.12 7.4 7.4.8 7.6 7.6.6 7.7 7.7.13 10.0 10.0.2 10.1 10.1.0 UTD on Cisco IOS XE Software
In the following table, the left column lists Cisco software releases. The right column indicates whether a release is affected by the vulnerabilities that are described in this advisory and the first release that includes the fix for these vulnerabilities. Customers are advised to upgrade to an appropriate fixed software release as indicated in this section.
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
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The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerabilities that are described in this advisory.
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These vulnerabilities were found during internal security testing using existing testing processes as well as frontier AI models.
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To learn about 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.
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Show LessVersion Description Section Status Date 1.0 Initial public release. — Final 2026-OCT-21
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SOFTWARE DOWNLOADS AND TECHNICAL SUPPORT
The Cisco Support and Downloads page on Cisco.com provides information about 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 contact 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.