cisco-sa-snort3-vba-bufdos-jAuFdvn9MediumCVSS 5.8

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

Published
October 21, 2026
Last Modified
October 22, 2026

🔗 CVE IDs covered (1)

CVE-2026-20218 →

📋 Description

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 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 ["https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-notice-QGwHnJ6k"]. 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 ["https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-hardening-snort3-ybgmhTQe"].

CVE-2026-20218 — Cisco Secure Firewall Threat Defense Snort 3 Visual Basic for Applications Buffer Overflow Denial of Service Vulnerability (CVSS 3.1 5.8, CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L)

🎯 Affected products198

  • Cisco 3000 Series Industrial Security Appliances (ISA)
  • Cisco Firepower 1000 Series
  • Cisco Firepower 2100 Series
  • Cisco Firepower 4100 Series
  • Cisco Firepower 9000 Series
  • Cisco Open Source Snort3
  • Cisco Secure Firewall 1200 Series
  • Cisco Secure Firewall 200 Series
  • Cisco Secure Firewall 3100 Series
  • Cisco Secure Firewall 4200 Series
  • Cisco Secure Firewall 6100 Series
  • Cisco Secure Firewall Threat Defense (FTD) Software
  • Cisco Secure Firewall Threat Defense Virtual
  • Cisco UTD SNORT IPS Engine Software
  • Cisco Open Source Snort3 3.1.10.0
  • Cisco Open Source Snort3 3.1.12.0
  • Cisco Open Source Snort3 3.1.13.0
  • Cisco Open Source Snort3 3.1.14.0
  • Cisco Open Source Snort3 3.1.15.0
  • Cisco Open Source Snort3 3.1.16.0
  • Cisco Open Source Snort3 3.1.17.0
  • Cisco Open Source Snort3 3.1.18.0
  • Cisco Open Source Snort3 3.1.19.0
  • Cisco Open Source Snort3 3.1.2.0
  • Cisco Open Source Snort3 3.1.20.0
  • Cisco Open Source Snort3 3.1.21.0
  • Cisco Open Source Snort3 3.1.22.0
  • Cisco Open Source Snort3 3.1.23.0
  • Cisco Open Source Snort3 3.1.24.0
  • Cisco Open Source Snort3 3.1.25.0
  • +168 more not shown

✅ Remediation

Cisco has released software updates that address this vulnerability. https://software.cisco.com Workaround: 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 ["https://www.cisco.com/c/en/us/td/docs/security/secure-firewall/release-notes/threat-defense/720/threat-defense-release-notes-72.html#Cisco_Concept.dita_c09a8957-13ac-4b4e-bcae-a141acadd92d"] Snort 3 Inspector Reference ["https://www.cisco.com/go/snort3-inspectors"] Custom Snort 3 Intrusion Policies for Access Control ["https://www.cisco.com/c/en/us/td/docs/security/secure-firewall/management-center/snort/720/snort3-configuration-guide-v72.html"] 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. Workarounds: 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 ["https://www.cisco.com/c/en/us/td/docs/security/secure-firewall/release-notes/threat-defense/720/threat-defense-release-notes-72.html#Cisco_Concept.dita_c09a8957-13ac-4b4e-bcae-a141acadd92d"] Snort 3 Inspector Reference ["https://www.cisco.com/go/snort3-inspectors"] Custom Snort 3 Intrusion Policies for Access Control ["https://www.cisco.com/c/en/us/td/docs/security/secure-firewall/management-center/snort/720/snort3-configuration-guide-v72.html"] 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.

🔗 References (12)