# CVE-2021-34753: Cisco Firepower Threat Defense Ethernet Industrial Protocol Policy Bypass Vulnerabilities

> An unauthenticated remote attacker can bypass configured access control and intrusion policies for ENIP traffic by sending crafted packets.

- **Severity:** Medium 5.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Nov 2024
- **Updated:** 15 Nov 2024
- **Also known as:** GHSA-4383-m935-j5wh

## What is CVE-2021-34753?

CVE-2021-34753 is a medium-severity vulnerability in Cisco Secure Firewall Threat Defense, published on 15 Nov 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability in the payload inspection for Ethernet Industrial Protocol (ENIP) traffic for Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to bypass configured rules for ENIP traffic.

This vulnerability is due to incomplete processing during deep packet inspection for ENIP packets. An attacker could exploit this vulnerability by sending a crafted ENIP packet to the targeted interface. A successful exploit could allow the attacker to bypass configured access control and intrusion policies that should trigger and drop for the ENIP packet.

Weakness: CWE-284 (Improper Access Control)

## Which versions are affected by CVE-2021-34753?

It affects 1 product.


Products: Cisco Secure Firewall Threat Defense.

## How do I fix CVE-2021-34753?

No fix has been published for CVE-2021-34753 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-34753 being exploited?

There is no known exploitation of CVE-2021-34753 in the wild and no public exploit code.

## Other vulnerabilities in Cisco Secure Firewall Threat Defense

- [CVE-2024-20412](https://insights.sbomify.com/CVE-2024-20412/): Hardcoded credentials in Cisco Firepower Threat Defense Software (critical 9.3)
- [CVE-2024-20330](https://insights.sbomify.com/CVE-2024-20330/): Memory corruption in Cisco Firepower Threat Defense Software (high 8.6)
- [CVE-2024-20339](https://insights.sbomify.com/CVE-2024-20339/): Cisco Firepower Threat Defense Software for Firepower 2100 Series TLS Denial of Service Vulnerability (high 8.6)
- [CVE-2024-20351](https://insights.sbomify.com/CVE-2024-20351/): Cisco Firepower Threat Defense Software Snort Firewall Denial of Service Vulnerability (high 8.6)
- [CVE-2023-20083](https://insights.sbomify.com/CVE-2023-20083/): Denial of service in Cisco Firepower Threat Defense Software (high 8.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-34753 and fix it if it is affected.

What it is: CVE-2021-34753 is a medium-severity vulnerability in Cisco Secure Firewall Threat Defense, published on 15 Nov 2024. 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-2021-34753 in the wild and no public exploit code.

Affected product: Cisco Secure Firewall Threat Defense. 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-2021-34753/ (Markdown: https://insights.sbomify.com/CVE-2021-34753/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-34753
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-34753
- OSV: https://osv.dev/vulnerability/CVE-2021-34753

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-34753/
Summaries are generated and may contain mistakes; the official description above is the record.