# CVE-2021-34714: Multiple Cisco Operating Systems Unidirectional Link Detection Denial of Service Vulnerability

> An adjacent attacker can cause a denial of service by sending crafted UDLD packets to Cisco devices with the feature enabled.

- **Severity:** High 7.4 (`CVSS:3.1/AV:A/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:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 23 Sep 2021
- **Updated:** 7 Nov 2024
- **Also known as:** GHSA-wjvw-6gq9-r937

## What is CVE-2021-34714?

CVE-2021-34714 is a high-severity denial of service vulnerability in Cisco Firepower Extensible Operating System, published on 23 Sep 2021. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

A vulnerability in the Unidirectional Link Detection (UDLD) feature of Cisco FXOS Software, Cisco IOS Software, Cisco IOS XE Software, Cisco IOS XR Software, and Cisco NX-OS Software could allow an unauthenticated, adjacent attacker to cause an affected device to reload. This vulnerability is due to improper input validation of the UDLD packets. An attacker could exploit this vulnerability by sending specifically crafted UDLD packets to an affected device. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a denial of service (DoS) condition. Note: The UDLD feature is disabled by default, and the conditions to exploit this vulnerability are strict. An attacker must have full control of a directly connected device. On Cisco IOS XR devices, the impact is limited to the reload of the UDLD process.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2021-34714?

It affects 6 products.


Products: Cisco Firepower Extensible Operating System, Cisco Fxos, Cisco Ios, Cisco Ios Xe, Cisco Ios Xr, Cisco Nx-Os.

## How do I fix CVE-2021-34714?

No fix has been published for CVE-2021-34714 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-34714 being exploited?

There is no known exploitation of CVE-2021-34714 in the wild and no public exploit code.

## Other vulnerabilities in Cisco Firepower Extensible Operating System

- [CVE-2018-0310](https://insights.sbomify.com/CVE-2018-0310/): Information disclosure in Cisco FXOS and NX-OS unknown (critical 9.8)
- [CVE-2015-6435](https://insights.sbomify.com/CVE-2015-6435/): Command injection in n/a (critical 9.8)
- [CVE-2021-1368](https://insights.sbomify.com/CVE-2021-1368/): Memory corruption in Cisco NX-OS Software (high 8.8)
- [CVE-2020-3456](https://insights.sbomify.com/CVE-2020-3456/): Cisco FXOS Software Firepower Chassis Manager Cross-Site Request Forgery Vulnerability (high 8.8)
- [CVE-2020-3172](https://insights.sbomify.com/CVE-2020-3172/): Cisco FXOS and NX-OS Software Cisco Discovery Protocol Arbitrary Code Execution and Denial of Service Vulnerability (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-34714 and fix it if it is affected.

What it is: CVE-2021-34714 is a high-severity denial of service vulnerability in Cisco Firepower Extensible Operating System, published on 23 Sep 2021. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-34714 in the wild and no public exploit code.

Affected product: Cisco Firepower Extensible Operating System. 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-2021-34714/ (Markdown: https://insights.sbomify.com/CVE-2021-34714/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-34714
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-34714
- OSV: https://osv.dev/vulnerability/CVE-2021-34714

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-34714/
Summaries are generated and may contain mistakes; the official description above is the record.