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Advisory severityMedium5.8Cisco Updated

Medium [CVE-2026-20218] Multiple Cisco Products Snort 3 Visual Basic for Applications Buffer Overflow Denial of Service Vulnerability

This medium-severity Cisco advisory covers CVE-2026-20218 affecting Secure Firewall Threat Defense (FTD) Software, Firepower 2100 Series, Firepower 1000 Series.

Aggregated and source-linked by VulniPulse. Data sources, validation and limitations.

cisco-sa-snort3-vba-bufdos-jAuFdvn9 Source published Source updated

VulniPulse record published Record updated

CVE-2026-20218
Affected products & platforms
CiscoFirewallASA / Firepower
Open source advisory

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Summary

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.

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.

Affected products named by the advisory: Secure Firewall Threat Defense (FTD) Software; Firepower 2100 Series; Firepower 1000 Series; 3000 Series Industrial Security Appliances (ISA); and 4 more.

Affected versions
  • Scope: For information about which products were affected by this vulnerability at the time of publication, see the following sections. Open Source Snort 3
  • Release 3.x (first fixed: 3.12.4.0)
  • Release 17.12 (first fixed: 17.12.8)
  • Release 17.15 (first fixed: 17.15.6)
  • Release 17.18 (first fixed: 17.18.5)
  • Release 26.1 (first fixed: 26.1.2)
  • Release 26.2 (first fixed: 26.2.1)

Official advisory · high-confidence parse· fetched 16 hours ago·verify at source

Fixed versions
  • 3.12.4.0
  • 17.12.8
  • 17.15.6
  • 17.18.5
  • 26.1.2
  • 26.2.1

Official advisory · high-confidence parse· fetched 16 hours ago·verify at source

Mitigation checklist

Recommended fix / mitigation
  • Upgrade to the first fixed release for your train per the Fixed Releases table in this advisory.
  • Release 3.x: upgrade to 3.12.4.0.
  • Release 17.12: upgrade to 17.12.8.
  • Release 17.15: upgrade to 17.15.6.
  • Release 17.18: upgrade to 17.18.5.
  • Release 26.1: upgrade to 26.1.2.
  • Release 26.2: upgrade to 26.2.1.
Temporary 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
  • 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 depl…

Official advisory · high-confidence parse· fetched 16 hours ago·verify at source

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