---
id: "CVE-2026-20011"
kind: "vulnerability"
aliases: ["CVE-2026-20011"]
title: "Cisco Snort 3: crafted SMTP MIME headers crash the detection engine"
severity: "medium"
cvss: 5.8
epss: 0.00416
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["cisco", "infrastructure", "network-security", "smtp", "snort"]
not_affected_if: ["snort-not-deployed"]
published_at: "2026-10-21T17:18:26+00:00"
first_seen_at: "2026-10-23T21:57:29+00:00"
updated_at: "2026-10-25T04:10:05+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-20011", "first_seen_at": "2026-10-23T21:57:29+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-20011", "first_seen_at": "2026-10-24T13:15:54+00:00"}]
---

# Cisco Snort 3: crafted SMTP MIME headers crash the detection engine

Snort 3 in multiple Cisco products fails to check errors while parsing MIME fields in SMTP headers. A remote, unauthenticated attacker can send crafted SMTP traffic to make the Snort 3 Detection Engine restart, causing denial of service.

_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-2026-20011
- 2026-10-24T13:15:54+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-20011

## From the sources

Multiple Cisco products are affected by a vulnerability in the Snort 3 SMTP MIME Decoder that could allow an unauthenticated, remote attacker to cause the Snort 3 Detection Engine to restart.

This vulnerability is due to a lack of error checking when the MIME fields of the SMTP header are parsed. An attacker could exploit this vulnerability by sending crafted SMTP packets through an established connection to be parsed by Snort 3. A successful exploit could allow the attacker to cause a denial of service (DoS) condition when the Snort 3 Detection Engine unexpectedly restarts.

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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_