dbcve.org
Sf200 24 FirmwareOperating system · Cisco

CVE-2021-40127

MEDIUM · 5.3 CVSS v3.1 Published 2021-11-04
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
62/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

This vulnerability in Cisco Small Business switch web management interfaces allows unauthenticated remote attackers to send specially crafted HTTP requests that cause a permanent invalid redirect, rendering the web interface completely unusable for legitimate management access.

MitigationApply Cisco firmware updates when available; until then, restrict access to the web-based management interface using network ACLs or firewall rules to prevent unauthenticated HTTP access.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Sf200 24 FirmwareOperating system
Affected:all versions
Sf200 24fp FirmwareOperating system
Affected:all versions
Sf200 24p FirmwareOperating system
Affected:all versions
Sf200 48 FirmwareOperating system
Affected:all versions
Sf200 48p FirmwareOperating system
Affected:all versions
Sf200e 24 FirmwareOperating system
Affected:all versions
Sf200e 24p FirmwareOperating system
Affected:all versions
Sf200e 48 FirmwareOperating system
Affected:all versions

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify your switch model
    Check the device model number on the physical device label or run 'show version' command via console/SSH to confirm the exact model
    Affected if The model is one of: Sf200 24, Sf200 24fp, Sf200 24p, Sf200 48, Sf200 48p, Sf200e 24, Sf200e 24p, or Sf200e 48
  2. Verify if the web management interface is enabled
    Check the HTTP server configuration via the web UI under Administration > Management Interface > HTTP Settings, or via CLI with 'show http server status'
    Affected if HTTP or HTTPS web management is enabled
  3. Confirm web interface accessibility from untrusted networks
    Review your network ACLs, firewall rules, or VLAN configuration to determine if the management IP is reachable from outside your trusted management network
    Affected if The web interface IP is accessible from untrusted networks or the internet without ACL restrictions
  4. Test for the invalid redirect symptom
    Attempt to access the web management interface via HTTP/HTTPS and observe the response; a successful attack results in a permanent redirect to an invalid or unreachable URL that prevents normal login
    Affected if Accessing the web interface returns a permanent redirect to an invalid URL or fails to load the login page
  5. Review firmware version
    Check the current firmware version via the web UI under Administration > Firmware > Upload, or via CLI with 'show firmware version'
    Affected if The firmware version is any version (all versions of the listed models are affected)

You are affected if you own any of the listed Sf200/Sf200e switch models with the web management interface enabled and accessible from untrusted networks, as all firmware versions are vulnerable to this unauthenticated attack that breaks the web interface.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply Cisco firmware updates when available; until then, restrict access to the web-based management interface using network ACLs or firewall rules to prevent unauthenticated HTTP access.

Fix this in Sf200 24 Firmware Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing4.0 h
  • Review / QA2.0 h
18.0 hours of engineering $3,200
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-40127 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data