CVE-2021-40127

What it is

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.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Exploit odds

1.3% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-11-04 16:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 04:06 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 1.3% in the next 30 days (EPSS).
• Severity: 5.3 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-11-04 16:15 UTC

Last modified

2026-06-17 04:06 UTC

Exploit probability

1.3% · EPSS, next 30 days

Weakness

CWE-20 · Improper input validation

Record status

Modified

Affected

• 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

Attack profile CVSS 3.1 · 5.3

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

Low

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-40127.md and follow it. Check whether this project is affected by CVE-2021-40127. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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