---
id: "CVE-2026-20197"
kind: "vulnerability"
aliases: ["CVE-2026-20197"]
title: "Cisco Snort 3: crafted Teredo packet crashes packet inspection engine"
severity: "medium"
cvss: 5.8
epss: 0.0039
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["cisco", "ids-ips", "infrastructure", "network-security", "snort-3"]
not_affected_if: ["no-teredo-inspection", "snort-2"]
published_at: "2026-10-21T17:18:27+00:00"
first_seen_at: "2026-10-23T21:57:29+00:00"
updated_at: "2026-10-25T04:10:03+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-20197", "first_seen_at": "2026-10-23T21:57:29+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-20197", "first_seen_at": "2026-10-24T13:15:54+00:00"}]
---

# Cisco Snort 3: crafted Teredo packet crashes packet inspection engine

Snort 3, the intrusion detection engine shipped in several Cisco products, mishandles certain Teredo tunnel packets because error checking is incomplete. A remote attacker without credentials can send one crafted packet to make the Snort 3 detection engine restart, interrupting packet inspection.

_Summary, check and fix written by a model from the sources; labelled as such._

## Timeline

- 2026-10-23T21:57:29+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-20197
- 2026-10-24T13:15:54+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-20197

## From the sources

Multiple Cisco products are affected by a vulnerability in the Snort 3 Teredo Detection Engine that could allow an unauthenticated, remote attacker to cause the Snort 3 Detection Engine to restart, resulting in an interruption of packet inspection.

This vulnerability is due to incomplete error checking when Snort 3 parses Teredo packets. An attacker could exploit this vulnerability by sending a crafted Teredo packet to a targeted device to be parsed by Snort. A successful exploit could allow the attacker to cause the Snort 3 Detection Engine to restart unexpectedly, resulting in a DoS condition.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_