CVE-2021-20599Network attack vector

Unauthorized login via cleartext non-password credentials

Published Oct 14, 2021 · Updated Aug 3, 2024

Cleartext credential exposure in MELSEC iQ-R Safety CPU 26 and earlier and SIL2 Process CPU 11 and earlier allows remote attackers to log in. The CPU module transmits non-password authentication credentials in cleartext, allowing network observers to recover values accepted by its login mechanism. Network access to the module's communications is sufficient; successful use grants unauthorized CPU-module access with confidentiality and integrity consequences.

CVSS severity9.1
Critical
EPSS probability1.40%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cleartext credential exposure in MELSEC iQ-R Safety CPU 26 and earlier and SIL2 Process CPU 11 and earlier allows remote attackers to log in. The CPU module transmits non-password authentication credentials in cleartext, allowing network observers to recover values accepted by its login mechanism. Network access to the module's communications is sufficient; successful use grants unauthorized CPU-module access with confidentiality and integrity consequences.

The record

CVE
CVE-2021-20599
Published
Oct 14, 2021
Updated
Aug 3, 2024
Vendor
Mitsubishi Electric Corporation
Product
MELSEC iQ-R Series Safety CPU R120SFCPU
Classifications
CWE-319, CAPEC-115, T0859
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 14, 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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=-
  2. Affected versionversion=Firmware versions "26" and prior

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mitsubishi Electric Corporation · MELSEC iQ-R Series Safety CPU R120SFCPUversion=-; version=Firmware versions "26" and prior
Mitsubishi Electric Corporation · MELSEC iQ-R Series Safety CPU R16SFCPUversion=-; version=Firmware versions "26" and prior
Mitsubishi Electric Corporation · MELSEC iQ-R Series SIL2 Process CPU R08PSFCPUversion=-; version=Firmware versions "11" and prior
Mitsubishi Electric Corporation · MELSEC iQ-R Series SIL2 Process CPU R120PSFCPUversion=-; version=Firmware versions "11" and prior
Mitsubishi Electric Corporation · MELSEC iQ-R Series Safety CPU R08SFCPUversion=-; version=Firmware versions "26" and prior
Mitsubishi Electric Corporation · MELSEC iQ-R Series SIL2 Process CPU R16PSFCPUversion=-; version=Firmware versions "11" and prior
Mitsubishi Electric Corporation · MELSEC iQ-R Series SIL2 Process CPU R32PSFCPUversion=-; version=Firmware versions "11" and prior
Mitsubishi Electric Corporation · MELSEC iQ-R Series Safety CPU R32SFCPUversion=-; version=Firmware versions "26" and prior

Published CVSS scores

9.1Mitsubishi Electric CorporationCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

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 11, 2026Sep 17, 2026
Latest reporting daySep 17, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-319Cleartext Transmission of Sensitive Information
CAPEC-115Authentication Bypass
T0859Valid Accounts

Public exploit references

No public exploit references are available in this record.

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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