CVE-2021-20598Public exploitNetwork attack vector

Unauthenticated account lockout via repeated failed logins

Published Aug 6, 2021 · Updated Aug 3, 2024

Account lockout in Mitsubishi Electric MELSEC iQ-R Series CPU Modules, all versions, allows remote attackers to deny legitimate logins. The login mechanism applies its lockout threshold to repeated incorrect password submissions without authenticating the requester. Network access to the login service is sufficient; repeated failed password attempts prevent the account holder from logging in but do not stop PLC operation.

CVSS severity3.7
Low
EPSS probability1.51%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Account lockout in Mitsubishi Electric MELSEC iQ-R Series CPU Modules, all versions, allows remote attackers to deny legitimate logins. The login mechanism applies its lockout threshold to repeated incorrect password submissions without authenticating the requester. Network access to the login service is sufficient; repeated failed password attempts prevent the account holder from logging in but do not stop PLC operation.

The record

CVE
CVE-2021-20598
Published
Aug 6, 2021
Updated
Aug 3, 2024
Vendor
Mitsubishi Electric Corporation
Product
MELSEC iQ-R Series CPU Modules
Classifications
CWE-287, CWE-645, T1531
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 6, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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=all versions

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mitsubishi Electric Corporation · MELSEC iQ-R Series CPU Modulesversion=all versions

Published CVSS scores

3.7Mitsubishi Electric CorporationCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
5.0NIST National Vulnerability DatabaseAV:N/AC:L/Au:N/C:N/I:N/A:P
5.3NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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 exploitPublished

Weakness, pattern, technique

CWE-287Improper Authentication
CWE-645Overly Restrictive Account Lockout Mechanism
T1531Account Access Removal

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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