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

Multiple Cisco products

A vulnerability in the Snort 3 Visual Basic for Applications Decompression Engine of multiple Cisco products could allow an unauthenticated, remote attacker to cause the Snort 3 Detection Engine to restart unexpectedly.

Fix it

Upgrade to Open Source Snort 3 3.12.4.0

First seen: 22 Oct 2026
Last update: 22 Oct 2026, 19:03 UTC
Fixed in: 3.12.4.0
Identifiers: CVE-2026-20218
CVSS: 5.8
Source: news
On the menu as: VPN & firewalls

Check this repository for exposure to one security incident from pwned.coffee. Report first, change nothing until I say so.

## Cisco Products Snort 3 Visual Basic for Applications Buffer Overflow Denial of Service Vulnerability
Severity: medium. Patch status: patched.
Affected: Multiple Cisco products
Fixed in: 3.12.4.0
Ids: CVE-2026-20218

A vulnerability in the Snort 3 Visual Basic for Applications Decompression Engine of multiple Cisco products could allow an unauthenticated, remote attacker to cause the Snort 3 Detection Engine to restart unexpectedly.

## Steps
1. This touches infrastructure (vpn-edge). Look in terraform, ansible, cloud-init, Dockerfiles and docs for the product and version we run. If it isn't in the repo, say so and list what a human should check on the box.
2. Fix by release line: Open Source Snort 3: 3.12.4.0.

## Fix by release line
| Line | State | Fix | Until then |
|---|---|---|---|
| Open Source Snort 3 | fixed | 3.12.4.0 | — |

## Report
A table: file, product or package, version in use, affected yes/no, exact fix. Then anything a human has to check outside the repo.

If you have the pwned.coffee MCP server (https://pwned.coffee/mcp), call lookup_cve("CVE-2026-20218") for the latest, and check_repo with this repo's lockfiles, Dockerfiles and workflows for a full receipt.
Sources: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-snort3-vba-bufdos-jAuFdvn9?vs_f=Cisco%20Security%20Advisory%26vs_cat=Security%20Intelligence%26vs_type=RSS%26vs_p=Multiple%20Cisco%20Products%20Snort%203%20Visual%20Basic%20for%20Applications%20Buffer%20Overflow%20Denial%20of%20Service%20Vulnerability%26vs_k=1
https://pwned.coffee/i/cisco-products-snort-3-visual-basic-for-applications-buf-cve-2026-20218

Receipt

Exploitation: No known exploitation
Fix by release line: Product Affected Fixed in Source
Open Source Snort 3 before 3.12.4.0 3.12.4.0 Vendor advisory checked 10 Nov
Score: CVSS 5.8 (medium). CVSS 3.1 5.8 (CNA cisco) for CVE-2026-20218
Last checked: 10 Nov 2026, 09:19 UTC

Product	Affected	Fixed in	Source
Open Source Snort 3	before 3.12.4.0	3.12.4.0	Vendor advisory checked 10 Nov

Sources: KEV – CVE record ✓ Vendor ✓

Sources

sec.cloudapps.cisco.com: Multiple Cisco Products Snort 3 Visual Basic for Applications Buffer Overflow Denial of Service Vulnerability

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