# CVE-2021-1621: Cisco IOS XE Software Interface Queue Wedge Denial of Service Vulnerability

> An unauthenticated adjacent attacker can cause a denial of service by sending specific Layer 2 frames to a Cisco IOS XE router.

- **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-7pgq-9248-43gw

## What is CVE-2021-1621?

CVE-2021-1621 is a high-severity denial of service vulnerability in Cisco Ios Xe, 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 Layer 2 punt code of Cisco IOS XE Software could allow an unauthenticated, adjacent attacker to cause a queue wedge on an interface that receives specific Layer 2 frames, resulting in a denial of service (DoS) condition. This vulnerability is due to improper handling of certain Layer 2 frames. An attacker could exploit this vulnerability by sending specific Layer 2 frames on the segment the router is connected to. A successful exploit could allow the attacker to cause a queue wedge on the interface, resulting in a DoS condition.

Weakness: CWE-399

## Which versions are affected by CVE-2021-1621?

It affects 1 product.


Products: Cisco Ios Xe.

## How do I fix CVE-2021-1621?

No fix has been published for CVE-2021-1621 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-1621 being exploited?

There is no known exploitation of CVE-2021-1621 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-2021-1621 and fix it if it is affected.

What it is: CVE-2021-1621 is a high-severity denial of service vulnerability in Cisco Ios Xe, 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-2021-1621 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-2021-1621/ (Markdown: https://insights.sbomify.com/CVE-2021-1621/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-1621
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-1621
- OSV: https://osv.dev/vulnerability/CVE-2021-1621

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-1621/
Summaries are generated and may contain mistakes; the official description above is the record.