# CVE-2021-40127: Cisco Small Business 200, 300, and 500 Series Switches Web-Based Management Interface Denial of Service Vulnerability

> Unauthenticated remote attackers can cause a permanent denial of service on the web management interface of Cisco Small Business switches via crafted HTTP requests.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 4 Nov 2021
- **Updated:** 7 Nov 2024
- **Also known as:** GHSA-mq2g-mwpw-5386

## What is CVE-2021-40127?

CVE-2021-40127 is a medium-severity denial of service vulnerability in Cisco Small Business Smart and Managed Switches, published on 4 Nov 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

A vulnerability in the web-based management interface of Cisco Small Business 200 Series Smart Switches, Cisco Small Business 300 Series Managed Switches, and Cisco Small Business 500 Series Stackable Managed Switches could allow an unauthenticated, remote attacker to render the web-based management interface unusable, resulting in a denial of service (DoS) condition. This vulnerability is due to improper validation of HTTP requests. An attacker could exploit this vulnerability by sending a crafted HTTP request to an affected device. A successful exploit could allow the attacker to cause a permanent invalid redirect for requests sent to the web-based management interface of the device, resulting in a DoS condition.

Weakness: CWE-20 (Improper Input Validation)

## Which versions are affected by CVE-2021-40127?

It affects 66 products.


Products: Cisco Sf200-24 Firmware, Cisco Sf200-24fp Firmware, Cisco Sf200-24p Firmware, Cisco Sf200-48 Firmware, Cisco Sf200-48p Firmware, Cisco Sf200e-24 Firmware, Cisco Sf200e-24p Firmware, Cisco Sf200e-48 Firmware, Cisco Sf200e-48p Firmware, Cisco Sf300-08 Firmware, Cisco Sf300-24 Firmware, Cisco Sf300-24mp Firmware, Cisco Sf300-24p Firmware, Cisco Sf300-24pp Firmware, Cisco Sf300-48 Firmware, Cisco Sf300-48p Firmware, Cisco Sf300-48pp Firmware, Cisco Sf302-08 Firmware, Cisco Sf302-08mp Firmware, Cisco Sf302-08mpp Firmware and 46 more.

## How do I fix CVE-2021-40127?

No fix has been published for CVE-2021-40127 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-40127 being exploited?

There is no known exploitation of CVE-2021-40127 in the wild and no public exploit code.

## Other vulnerabilities in Cisco Small Business Smart and Managed Switches

- [CVE-2018-15439](https://insights.sbomify.com/CVE-2018-15439/): Cisco Small Business Switches Privileged Access Vulnerability (critical 9.8)
- [CVE-2020-3363](https://insights.sbomify.com/CVE-2020-3363/): Cisco Small Business Smart and Managed Switches Denial of Service Vulnerability (high 8.6)
- [CVE-2020-3297](https://insights.sbomify.com/CVE-2020-3297/): Cisco Small Business Smart and Managed Switches Session Management Vulnerability (high 8.1)
- [CVE-2019-12636](https://insights.sbomify.com/CVE-2019-12636/): Cisco Small Business Smart and Managed Switches Cross-Site Request Forgery Vulnerability (high 8.1)
- [CVE-2019-15993](https://insights.sbomify.com/CVE-2019-15993/): Cisco Small Business Switches Information Disclosure Vulnerability (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-40127 and fix it if it is affected.

What it is: CVE-2021-40127 is a medium-severity denial of service vulnerability in Cisco Small Business Smart and Managed Switches, published on 4 Nov 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-2021-40127 in the wild and no public exploit code.

Affected product: Cisco Small Business Smart and Managed Switches. 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-2021-40127/ (Markdown: https://insights.sbomify.com/CVE-2021-40127/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-40127
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-40127
- OSV: https://osv.dev/vulnerability/CVE-2021-40127

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From sbomify Insights: https://insights.sbomify.com/CVE-2021-40127/
Summaries are generated and may contain mistakes; the official description above is the record.