# CVE-2026-20011: Multiple Cisco Products Snort 3 SMTP MIME Denial of Service Vulnerability


- **Severity:** Medium 5.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 21 Oct 2026
- **Updated:** 22 Oct 2026
- **Also known as:** GHSA-mj78-cj39-7cv9

## What is CVE-2026-20011?

CVE-2026-20011 is a medium-severity vulnerability in Cisco Open Source Snort3, published on 21 Oct 2026. 

### Official description

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.

Weakness: CWE-805 (Buffer Access with Incorrect Length Value)

## Which versions are affected by CVE-2026-20011?


## How do I fix CVE-2026-20011?

No fix has been published for CVE-2026-20011 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-20011 being exploited?

There is no known exploitation of CVE-2026-20011 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-20011 and fix it if it is affected.

What it is: CVE-2026-20011 is a medium-severity vulnerability in Cisco Open Source Snort3, published on 21 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-20011 in the wild and no public exploit code.

Affected product: Cisco Open Source Snort3. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-20011/ (Markdown: https://insights.sbomify.com/CVE-2026-20011/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-20011
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-20011
- OSV: https://osv.dev/vulnerability/CVE-2026-20011

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-20011/
Summaries are generated and may contain mistakes; the official description above is the record.