# CVE-2021-40116: Multiple Cisco Products Snort Rule Denial of Service Vulnerability

> Remote attackers can cause denial of service on Cisco Firepower devices by sending crafted packets if specific Snort3 rules are configured.

- **Severity:** High 8.6 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 27 Oct 2021
- **Updated:** 7 Nov 2024
- **Also known as:** GHSA-w5gp-j3p5-92ch

## What is CVE-2021-40116?

CVE-2021-40116 is a high-severity denial of service vulnerability in Cisco Secure Firewall Management Center, published on 27 Oct 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Multiple Cisco products are affected by a vulnerability in Snort rules that could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device.The vulnerability is due to improper handling of the Block with Reset or Interactive Block with Reset actions if a rule is configured without proper constraints. An attacker could exploit this vulnerability by sending a crafted IP packet to the affected device. A successful exploit could allow the attacker to cause through traffic to be dropped. Note: Only products with Snort3 configured and either a rule with Block with Reset or Interactive Block with Reset actions configured are vulnerable. Products configured with Snort2 are not vulnerable.

Weakness: CWE-241 (Improper Handling of Unexpected Data Type)

## Which versions are affected by CVE-2021-40116?

It affects 3 products.


Products: Cisco Secure Firewall Management Center, Cisco Secure Firewall Threat Defense, Cisco Snort.

## How do I fix CVE-2021-40116?

No fix has been published for CVE-2021-40116 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-40116 being exploited?

There is no known exploitation of CVE-2021-40116 in the wild and no public exploit code.

## Other vulnerabilities in Cisco Secure Firewall Management Center

- [CVE-2026-20079](https://insights.sbomify.com/CVE-2026-20079/): Cisco Firewall Management Center Authentication Bypass Using an Alternate Path or Channel (critical 10.0, exploited in the wild)
- [CVE-2026-20131](https://insights.sbomify.com/CVE-2026-20131/): Cisco Secure Firewall Management Center (FMC) Software and Cisco Security Cloud Control (SCC) Firewall Management Deserialization of Untrusted Data (critical 10.0, exploited in the wild)
- [CVE-2026-20316](https://insights.sbomify.com/CVE-2026-20316/): Cisco Secure Firewall Management Center Use of Hard-coded Password (medium 5.3, exploited in the wild)
- [CVE-2025-20265](https://insights.sbomify.com/CVE-2025-20265/): Cisco Secure Firewall Management Center Software Radius Remote Code Execution Vulnerability (critical 10.0)
- [CVE-2024-20424](https://insights.sbomify.com/CVE-2024-20424/): Command injection in Cisco Firepower Management Center (critical 9.9)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-40116 and fix it if it is affected.

What it is: CVE-2021-40116 is a high-severity denial of service vulnerability in Cisco Secure Firewall Management Center, published on 27 Oct 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-40116 in the wild and no public exploit code.

Affected product: Cisco Secure Firewall Management Center. 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-2021-40116/ (Markdown: https://insights.sbomify.com/CVE-2021-40116/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-40116
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-40116
- OSV: https://osv.dev/vulnerability/CVE-2021-40116

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-40116/
Summaries are generated and may contain mistakes; the official description above is the record.