# CVE-2021-1439: Cisco Aironet Access Points FlexConnect Multicast DNS Denial of Service Vulnerability

> An adjacent attacker can cause a denial of service on Cisco Aironet Access Points by sending crafted mDNS packets, requiring FlexConnect local switching or mDNS VLAN configuration.

- **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:** 24 Mar 2021
- **Updated:** 8 Nov 2024
- **Also known as:** GHSA-2p9c-p5jq-7j4g

## What is CVE-2021-1439?

CVE-2021-1439 is a high-severity denial of service vulnerability in Cisco Aironet Access Point Software (IOS XE Controller), published on 24 Mar 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 multicast DNS (mDNS) gateway feature of Cisco Aironet Series Access Points Software could allow an unauthenticated, adjacent attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to insufficient input validation of incoming mDNS traffic. An attacker could exploit this vulnerability by sending a crafted mDNS packet to an affected device through a wireless network that is configured in FlexConnect local switching mode or through a wired network on a configured mDNS VLAN. A successful exploit could allow the attacker to cause the access point (AP) to reboot, resulting in a DoS condition.

Weakness: CWE-120 (Buffer Copy without Checking Size of Input)

## Which versions are affected by CVE-2021-1439?

It affects 2 products.


Products: Cisco Aironet Access Point Software, Cisco Catalyst 9800 Firmware.

## How do I fix CVE-2021-1439?

No fix has been published for CVE-2021-1439 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-1439 being exploited?

There is no known exploitation of CVE-2021-1439 in the wild and no public exploit code.

## Other vulnerabilities in Cisco Aironet Access Point Software (IOS XE Controller)

- [CVE-2017-3831](https://insights.sbomify.com/CVE-2017-3831/): Auth bypass in Cisco Mobility Express 1800 Access Point Series (critical 9.8)
- [CVE-2022-20622](https://insights.sbomify.com/CVE-2022-20622/): Cisco Embedded Wireless Controller with Catalyst Access Points IP Flood Denial of Service Vulnerability (high 8.6)
- [CVE-2018-0234](https://insights.sbomify.com/CVE-2018-0234/): Denial of service in Cisco Aironet 1810, 1830, and 1850 Series Access Points (high 8.6)
- [CVE-2016-1419](https://insights.sbomify.com/CVE-2016-1419/): Denial of service in n/a (high 8.1)
- [CVE-2016-6362](https://insights.sbomify.com/CVE-2016-6362/): Privilege escalation in n/a (high 7.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-1439 and fix it if it is affected.

What it is: CVE-2021-1439 is a high-severity denial of service vulnerability in Cisco Aironet Access Point Software (IOS XE Controller), published on 24 Mar 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-2021-1439 in the wild and no public exploit code.

Affected product: Cisco Aironet Access Point Software (IOS XE Controller). 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-2021-1439/ (Markdown: https://insights.sbomify.com/CVE-2021-1439/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-1439
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-1439
- OSV: https://osv.dev/vulnerability/CVE-2021-1439

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-1439/
Summaries are generated and may contain mistakes; the official description above is the record.