# CVE-2026-20221: Multiple Cisco Products Snort 3 Generic Routing Encapsulation Denial of Service Vulnerabilities


- **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-vm6m-qmxg-cg2c

## What is CVE-2026-20221?

CVE-2026-20221 is a medium-severity vulnerability in Cisco Cyber Vision, published on 21 Oct 2026. 

### Official description

Multiple Cisco products are affected by a vulnerability in the generic routing encapsulation (GRE) tunnel decapsulation feature of the Snort 3 Detection Engine that could allow an unauthenticated, remote attacker to cause an unexpected restart of the Snort 3 Detection Engine.

This vulnerability is due to improper handling of nested GRE traffic. An attacker could exploit this vulnerability by sending a crafted GRE payload through an affected device. A successful exploit could allow the attacker to trigger an unexpected reload of the Snort 3 Detection Engine, resulting in either a bypass or denial of service (DoS) condition, depending on device configuration. For more information, see the  section of this advisory. The Snort 3 Detection Engine will restart automatically. No manual intervention is required.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2026-20221?


## How do I fix CVE-2026-20221?

No fix has been published for CVE-2026-20221 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-20221 being exploited?

There is no known exploitation of CVE-2026-20221 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-20221 and fix it if it is affected.

What it is: CVE-2026-20221 is a medium-severity vulnerability in Cisco Cyber Vision, published on 21 Oct 2026. 
Exploitation: There is no known exploitation of CVE-2026-20221 in the wild and no public exploit code.

Affected product: Cisco Cyber Vision. 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-2026-20221/ (Markdown: https://insights.sbomify.com/CVE-2026-20221/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-20221
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-20221
- OSV: https://osv.dev/vulnerability/CVE-2026-20221

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-20221/
Summaries are generated and may contain mistakes; the official description above is the record.