LiveActive security incident?Get immediate response
CVE Record

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

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.

MediumCVSS 5.3Not KEV-listedUpdated
Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This issue can make the web management page on certain Cisco Small Business switches unusable. It does not expose data or directly change traffic, but it can block administrators from managing affected devices until corrected. Business impact is mainly operational disruption of network administration.

Executive priority

Treat this as a moderate operational-risk item. It is not a data-theft vulnerability, but exposed management interfaces can disrupt network administration. Prioritize inventory, management-plane access control, and vendor-guided remediation.

Technical view

CVE-2021-40127 is an unauthenticated remote DoS in the web-based management interface of Cisco Small Business 200, 300, and 500 Series switches. Improper HTTP request validation can cause a permanent invalid redirect for management-interface requests. CVSS 3.1 is 5.3, availability impact only.

Likely exposure

Exposure is most likely where affected Cisco Small Business switch management interfaces are reachable from untrusted networks. Internet-exposed or broadly reachable management UIs carry higher operational risk. The provided sources do not identify specific affected firmware versions.

Exploitation context

The CVE describes unauthenticated remote exploitation through a crafted HTTP request. The source bundle does not report active exploitation, and the CVE is not marked as CISA KEV. No exploit prevalence evidence is provided.

Researcher notes

Evidence supports CWE-20 improper input validation in HTTP request handling. The described impact is limited to the web management interface DoS through invalid redirects. Sources do not provide exploit status, affected firmware detail, or confirmed fixed versions in the supplied bundle.

Mitigation direction

  • Inventory Cisco Small Business 200, 300, and 500 Series switches.
  • Restrict web management access to trusted admin networks or VPN.
  • Check Cisco’s advisory for affected firmware and vendor remediation guidance.
  • Monitor management-interface availability and administrator access failures.
  • Prioritize exposed management interfaces before internally isolated devices.

Validation and detection

  • Confirm switch models and firmware against Cisco’s advisory.
  • Identify whether web management is reachable from untrusted networks.
  • Review logs or monitoring for management UI redirect failures or outages.
  • Verify administrative recovery procedures for inaccessible web management.
  • Document exposed devices for remediation tracking.
Prepared
Confidence
high
Sources
3

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-20: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2021-40127 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
Medium
CVSS
5.3 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
0Timeline events
0ADP providers
2Source links

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
5.3CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L3.91.4Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

5.3Medium
CVSS 3.1 vector shape for CVE-2021-40127Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone
Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
CiscoCisco Small Business Smart and Managed Switchesn/aListed
Weakness

CWE details

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-20 · source CWE mapping

Improper Input Validation

Improper Input Validation represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.