# CVE-2021-21003: Denial of Service Vulnerability in Phoenix Contact FL SWITCH SMCS series products

> Attackers can cause denial of service for web, SNMP, and ICMP services on Phoenix Contact switches by sending fragmented TCP packets.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 25 Jun 2021
- **Updated:** 17 Sep 2024
- **Also known as:** GHSA-4567-7fw8-972r

## What is CVE-2021-21003?

CVE-2021-21003 is a medium-severity denial of service vulnerability in Phoenix Contact FL NAT, published on 25 Jun 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In Phoenix Contact FL SWITCH SMCS series products in multiple versions fragmented TCP-Packets may cause a Denial of Service of Web-, SNMP- and ICMP-Echo services. The switching functionality of the device is not affected.

Weakness: CWE-404 (Improper Resource Shutdown or Release)

## Which versions are affected by CVE-2021-21003?

It affects 15 products.


Products: Phoenixcontact Fl Nat Smn 8tx-M Firmware, Phoenixcontact Fl Nat Smn 8tx Firmware, Phoenixcontact Fl Switch Smcs 14tx\/2fx-Sm Firmware, Phoenixcontact Fl Switch Smcs 14tx\/2fx Firmware, Phoenixcontact Fl Switch Smcs 16tx Firmware, Phoenixcontact Fl Switch Smcs 4tx-Pn Firmware, Phoenixcontact Fl Switch Smcs 6gt\/2sfp Firmware, Phoenixcontact Fl Switch Smcs 6tx\/2sfp Firmware, Phoenixcontact Fl Switch Smcs 8gt Firmware, Phoenixcontact Fl Switch Smcs 8tx-Pn Firmware, Phoenixcontact Fl Switch Smcs 8tx Firmware, Phoenixcontact Fl Switch Smn 6tx\/2fx Firmware, Phoenixcontact Fl Switch Smn 6tx\/2fx Sm Firmware, Phoenixcontact Fl Switch Smn 6tx\/2pof-Pn Firmware, Phoenixcontact Fl Switch Smn 8tx-Pn Firmware.

## How do I fix CVE-2021-21003?

No fix has been published for CVE-2021-21003 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-21003 being exploited?

There is no known exploitation of CVE-2021-21003 in the wild and no public exploit code.

## Other vulnerabilities in Phoenix Contact FL NAT

- [CVE-2021-21005](https://insights.sbomify.com/CVE-2021-21005/): Race Condition Vulnerability in Phoenix Contact FL SWITCH SMCS series products (high 7.5)
- [CVE-2021-21004](https://insights.sbomify.com/CVE-2021-21004/): Cross-site Scripting Vulnerability in Phoenix Contact FL SWITCH SMCS series products (high 7.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21003 and fix it if it is affected.

What it is: CVE-2021-21003 is a medium-severity denial of service vulnerability in Phoenix Contact FL NAT, published on 25 Jun 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-2021-21003 in the wild and no public exploit code.

Affected product: Phoenix Contact FL NAT. 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-2021-21003/ (Markdown: https://insights.sbomify.com/CVE-2021-21003/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21003
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21003
- OSV: https://osv.dev/vulnerability/CVE-2021-21003

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-21003/
Summaries are generated and may contain mistakes; the official description above is the record.