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CVE Record

CVE-2021-31251: An authentication bypass in telnet server in BF-430 and BF431 232/422 TCP/IP Converter, BF-450M and SEMAC f...

An authentication bypass in telnet server in BF-430 and BF431 232/422 TCP/IP Converter, BF-450M and SEMAC from CHIYU Technology Inc allows obtaining a privileged connection with the target device by supplying a specially malformed request and an attacker may force the remote telnet server to believe that the user has already authenticated.

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2021-31251 is an authentication bypass in the Telnet service of several CHIYU Technology access-control and TCP/IP converter devices. A malformed request can make the device believe the user is already authenticated, potentially granting privileged access without valid credentials.

Executive priority

Prioritize discovery and Telnet exposure reduction. The business risk is unauthorized privileged access to physical-security or converter devices, but urgency is constrained by incomplete public severity and version data.

Technical view

The CVE describes a Telnet server authentication bypass affecting CHIYU BF-430, BF431 232/422 TCP/IP Converter, BF-450M, and SEMAC devices. The record does not provide CVSS, CWE, affected firmware versions, or a precise fixed version in the supplied bundle.

Likely exposure

Exposure is most likely where affected CHIYU devices have Telnet reachable from management networks, OT networks, or the internet. Exact firmware exposure cannot be determined from the supplied CVE metadata.

Exploitation context

The source bundle describes a malformed-request authentication bypass and links public research, but it does not show CISA KEV listing or confirmed active exploitation. Treat public Telnet reachability as the main risk indicator.

Researcher notes

Key gaps are missing CVSS, CWE, affected firmware ranges, and fixed version details in the supplied bundle. Validate against vendor firmware guidance and public research, but avoid assuming exploitation beyond the described authentication bypass.

Mitigation direction

  • Identify CHIYU BF-430, BF431, BF-450M, and SEMAC devices in asset inventories.
  • Check CHIYU firmware update guidance for applicable device updates.
  • Restrict Telnet access to trusted management hosts only.
  • Remove internet exposure for affected device management interfaces.
  • Monitor affected devices for unexpected privileged Telnet sessions.

Validation and detection

  • Confirm whether listed CHIYU models are present in production or OT environments.
  • Determine whether Telnet is enabled and reachable on those devices.
  • Review firmware versions against CHIYU’s firmware update notice.
  • Check perimeter and internal scans for exposed Telnet management services.
  • Review logs for unusual administrative access where available.
Prepared
Confidence
medium
Sources
5

Public sources used

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.

description · low confidence lookup

Credential and access behavior lookup

The CVE wording references authentication or credential exposure, so valid-account and credential-access review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2021-31251 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
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.

0CVSS vectors
0Timeline events
0ADP providers
4Source links

CVSS and timeline data

No CVSS vectors or timeline events were available in the normalized CVE source material.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
n/an/an/aListed
Weakness

CWE details

No CWE listed

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