# CVE-2021-21004: Cross-site Scripting Vulnerability in Phoenix Contact FL SWITCH SMCS series products

> Attackers can inject malicious code via LLDP frames into the web management interface, allowing execution in the client's browser.

- **Severity:** High 7.4 (`CVSS:3.1/AV:A/AC:L/PR:N/UI:R/S:C/C:L/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 25 Jun 2021
- **Updated:** 16 Sep 2024
- **Also known as:** GHSA-p92q-6vw3-958m

## What is CVE-2021-21004?

CVE-2021-21004 is a high-severity cross-site scripting vulnerability in Phoenix Contact FL NAT, published on 25 Jun 2021. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

In Phoenix Contact FL SWITCH SMCS series products in multiple versions an attacker may insert malicious code via LLDP frames into the web-based management which could then be executed by the client.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2021-21004?

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-2021-21004?

No fix has been published for CVE-2021-21004 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-21004 being exploited?

There is no known exploitation of CVE-2021-21004 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-2021-21003](https://insights.sbomify.com/CVE-2021-21003/): Denial of Service Vulnerability in Phoenix Contact FL SWITCH SMCS series products (medium 5.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-21004 and fix it if it is affected.

What it is: CVE-2021-21004 is a high-severity cross-site scripting vulnerability in Phoenix Contact FL NAT, published on 25 Jun 2021. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-21004 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-2021-21004/ (Markdown: https://insights.sbomify.com/CVE-2021-21004/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-21004
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-21004
- OSV: https://osv.dev/vulnerability/CVE-2021-21004

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-21004/
Summaries are generated and may contain mistakes; the official description above is the record.