CVE-2021-20591

highpriority · track · 31EPSS 0.015 · 74 %ileEUUS

grimoire priorityP2 · Scheduled

Exploitable?

—

no known exploitation

Likely / severe?

1.50% (74th) EPSS

CVSS 7.8 · high

Is it mine?

31 products

Check your exposure

Who says so?

4 sources

cnnvd · enisa_euvd · cisa_csaf_ot · nvd

EPSS · scored 2026-10-27

Uncontrolled Resource Consumption vulnerability in Mitsubishi Electric MELSEC iQ-R series CPU modules (R00/01/02CPU all versions, R04/08/16/32/120(EN)CPU all versions, R08/16/32/120SFCPU all versions, R08/16/32/120PCPU all versions, R08/16/32/120PSFCPU all versions) allows a remote unauthenticated attacker to prevent legitimate clients from connecting to the MELSOFT transmission port (TCP/IP) by not closing a connection properly, which may lead to a denial of service (DoS) condition.

remediations

Vendor fix, mitigation, or workaround guidance, as published by each source.

No vendor fix yet; a mitigation is available.

MitigationR00/01/02CPUcisa_csaf_ot
If Port 5007 of the MELSOFT transmission port (TCP/IP) is not used, set b2 to "1" in advance. See MELSEC iQ-R Ethernet User's Manual (Application) Appendix 3, Buffer Memory for more information.
MitigationR04/08/16/32/120(EN)CPUcisa_csaf_ot
If Port 5007 of the MELSOFT transmission port (TCP/IP) is not used, set b2 to "1" in advance. See MELSEC iQ-R Ethernet User's Manual (Application) Appendix 3, Buffer Memory for more information.
MitigationR08/16/32/120PCPUcisa_csaf_ot
If Port 5007 of the MELSOFT transmission port (TCP/IP) is not used, set b2 to "1" in advance. See MELSEC iQ-R Ethernet User's Manual (Application) Appendix 3, Buffer Memory for more information.
MitigationR08/16/32/120PSFCPUcisa_csaf_ot
If Port 5007 of the MELSOFT transmission port (TCP/IP) is not used, set b2 to "1" in advance. See MELSEC iQ-R Ethernet User's Manual (Application) Appendix 3, Buffer Memory for more information.
MitigationR08/16/32/120SFCPUcisa_csaf_ot
If Port 5007 of the MELSOFT transmission port (TCP/IP) is not used, set b2 to "1" in advance. See MELSEC iQ-R Ethernet User's Manual (Application) Appendix 3, Buffer Memory for more information.

cvss

Technical severity, 0–10. One row per scoring source.

7.8

010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–high · 5.3–7.8

v2.07.8highAV:N/AC:L/Au:N/C:N/I:N/A:Cprimary · NVD / NIST USexploitability 10 · impact 6.9

v3.17.5highCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hprimary · NVD / NIST USexploitability 3.9 · impact 3.6

v3.05.3mediumCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Lsecondary · CISA US

v3.16.9mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H/E:Usecondary · CVSS-BT (t0sche)

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-400USprimaryCWE-400US

affected products (31)

Products and version ranges known to be affected.

R00/01/02CPU: All versionsall versionscisa_csaf_otUS
R04/08/16/32/120(EN)CPU: All versionsall versionscisa_csaf_otUS
R08/16/32/120PCPU: All versionsall versionscisa_csaf_otUS
R08/16/32/120PSFCPU: All versionsall versionscisa_csaf_otUS
R08/16/32/120SFCPU: All versionsall versionscisa_csaf_otUS
Mitsubishi Electric R00/01/02CPUall versionscisa_csaf_otUS
Mitsubishi Electric R04/08/16/32/120(EN)CPUall versionscisa_csaf_otUS
Mitsubishi Electric R08/16/32/120PCPUall versionscisa_csaf_otUS
Mitsubishi Electric R08/16/32/120PSFCPUall versionscisa_csaf_otUS
Mitsubishi Electric R08/16/32/120SFCPUall versionscisa_csaf_otUS
n/a MELSEC iQ-R Series CPU Modules≤ R00/01/02CPU all versions, R04/08/16/32/120(EN)CPU all versions, R08/16/32/120SFCPU all versions, R08/16/32/120PCPU all versions, R08/16/32/120PSFCPU all versionsenisa_euvdEU
mitsubishielectric r00cpu firmwareall versionsnvdUScpe:2.3:o:mitsubishielectric:r00cpu_firmware:*:*:*:*:*:*:*:*
mitsubishielectric r01cpu firmwareall versionsnvdUScpe:2.3:o:mitsubishielectric:r01cpu_firmware:*:*:*:*:*:*:*:*
mitsubishielectric r02cpu firmwareall versionsnvdUScpe:2.3:o:mitsubishielectric:r02cpu_firmware:*:*:*:*:*:*:*:*
mitsubishielectric r04cpu firmwareall versionsnvdUScpe:2.3:o:mitsubishielectric:r04cpu_firmware:*:*:*:*:*:*:*:*
mitsubishielectric r08cpu firmwareall versionsnvdUScpe:2.3:o:mitsubishielectric:r08cpu_firmware:*:*:*:*:*:*:*:*
mitsubishielectric r08pcpu firmwareall versionsnvdUScpe:2.3:o:mitsubishielectric:r08pcpu_firmware:*:*:*:*:*:*:*:*
mitsubishielectric r08psfcpu firmwareall versionsnvdUScpe:2.3:o:mitsubishielectric:r08psfcpu_firmware:*:*:*:*:*:*:*:*
mitsubishielectric r08sfcpu firmwareall versionsnvdUScpe:2.3:o:mitsubishielectric:r08sfcpu_firmware:*:*:*:*:*:*:*:*
mitsubishielectric r120cpu firmwareall versionsnvdUScpe:2.3:o:mitsubishielectric:r120cpu_firmware:*:*:*:*:*:*:*:*

showing 20 of 31

advisories (1)

Vendor and ecosystem advisories describing this.

ICSA-21-147-05Mitsubishi Electric MELSEC iQ-R Series2021-05-27icsa · cisa_csaf_otUS
Successful exploitation of this vulnerability may prevent legitimate clients from connecting to an affected product.

also known as (3)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd cisa_csaf_ot nvd NVD CVE.org MITRE

published 2021-06-11modified 2026-06-17

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references (10)

External citations — patches, advisories, analysis.

scry

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