CVE-2021-40127Network attack vector

Web management service interrupt via invalid HTTP redirect

Published Nov 4, 2021 · Updated Nov 7, 2024

Improper HTTP request validation in Cisco Small Business 200, 300, and 500 Series Switches allows remote attackers to disable web management. The web-based management interface accepts a crafted HTTP request without proper validation and creates a permanent invalid redirect for later interface requests. No authentication or user interaction is required, and the resulting service interrupt prevents management access to the affected device.

CVSS severity5.3
Medium
EPSS probability1.28%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper HTTP request validation in Cisco Small Business 200, 300, and 500 Series Switches allows remote attackers to disable web management. The web-based management interface accepts a crafted HTTP request without proper validation and creates a permanent invalid redirect for later interface requests. No authentication or user interaction is required, and the resulting service interrupt prevents management access to the affected device.

The record

CVE
CVE-2021-40127
Published
Nov 4, 2021
Updated
Nov 7, 2024
Vendor
ClamAV
Product
Cisco Small Business Smart and Managed Switches
Classifications
CWE-20, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 4, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 7, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=n/a

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco Small Business Smart and Managed Switchesversion=n/a

Published CVSS scores

5.0NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:P
5.3Cisco Systems, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/E:X/RL:X/RC:X

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-20Improper Input Validation
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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