# CVE-2021-1446: Cisco IOS XE Software DNS NAT Protocol Application Layer Gateway Denial of Service Vulnerability

> Remote attackers can cause Cisco IOS XE devices to reload by sending crafted DNS packets through NAT, resulting in a denial of service.

- **Severity:** High 8.6 (`CVSS:3.1/AV:N/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:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 24 Mar 2021
- **Updated:** 8 Nov 2024
- **Also known as:** GHSA-m3m6-h5x2-mhf5

## What is CVE-2021-1446?

CVE-2021-1446 is a high-severity denial of service vulnerability in Cisco Ios Xe, published on 24 Mar 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability in the DNS application layer gateway (ALG) functionality used by Network Address Translation (NAT) in Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload. The vulnerability is due to a logic error that occurs when an affected device inspects certain DNS packets. An attacker could exploit this vulnerability by sending crafted DNS packets through an affected device that is performing NAT for DNS packets. A successful exploit could allow an attacker to cause the device to reload, resulting in a denial of service (DoS) condition on an affected device. The vulnerability can be exploited only by traffic that is sent through an affected device via IPv4 packets. The vulnerability cannot be exploited via IPv6 traffic.

Weakness: CWE-754 (Improper Check for Unusual or Exceptional Conditions)

## Which versions are affected by CVE-2021-1446?

It affects 1 product.


Products: Cisco Ios Xe.

## How do I fix CVE-2021-1446?

No fix has been published for CVE-2021-1446 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-1446 being exploited?

There is no known exploitation of CVE-2021-1446 in the wild and no public exploit code.

## Other vulnerabilities in Cisco Ios Xe

- [CVE-2023-20198](https://insights.sbomify.com/CVE-2023-20198/): Cisco IOS XE Web UI Privilege Escalation (critical 10.0, exploited in the wild)
- [CVE-2018-0151](https://insights.sbomify.com/CVE-2018-0151/): Cisco IOS Software and Cisco IOS XE Software Quality of Service Remote Code Execution (critical 9.8, exploited in the wild)
- [CVE-2023-20273](https://insights.sbomify.com/CVE-2023-20273/): Cisco IOS XE Web UI Command Injection (high 7.2, exploited in the wild)
- [CVE-2025-20188](https://insights.sbomify.com/CVE-2025-20188/): Hardcoded credentials in Cisco IOS XE Software (critical 10.0)
- [CVE-2021-34770](https://insights.sbomify.com/CVE-2021-34770/): Cisco IOS XE Software for Catalyst 9000 Family Wireless Controllers CAPWAP Remote Code Execution Vulnerability (critical 10.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-1446 and fix it if it is affected.

What it is: CVE-2021-1446 is a high-severity denial of service vulnerability in Cisco Ios Xe, published on 24 Mar 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-2021-1446 in the wild and no public exploit code.

Affected product: Cisco Ios Xe. 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-2021-1446/ (Markdown: https://insights.sbomify.com/CVE-2021-1446/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-1446
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-1446
- OSV: https://osv.dev/vulnerability/CVE-2021-1446

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-1446/
Summaries are generated and may contain mistakes; the official description above is the record.