How severe is CVE-2020-5666?

CVE-2020-5666 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2020-5666 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 8% (94th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2020-5666?

CVE-2020-5666 primarily affects Mitsubishielectric Melsec Iq-r00 Firmware. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2020-5666?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2020-5666 published?

CVE-2020-5666 was published on 2020-11-16 and last updated on 2026-06-17.

CVE-2020-5666

CVE-2020-5666 is a high-severity vulnerability in Mitsubishielectric Melsec Iq-r00 Firmware with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-400.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 7.1
EPSS exploit prediction: 8% (94th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-400
Affected product: Mitsubishielectric Melsec Iq-r00 Firmware
Published: 2020-11-16
Last modified: 2026-06-17

Description

Uncontrolled resource consumption vulnerability in MELSEC iQ-R Series CPU Modules (R00/01/02CPU Firmware versions from '05' to '19' and R04/08/16/32/120(EN)CPU Firmware versions from '35' to '51') allows a remote attacker to cause an error in a CPU unit via a specially crafted HTTP packet, which may lead to a denial-of-service (DoS) condition in execution of the program and its communication.

Frequently asked questions

What is CVE-2020-5666?: Uncontrolled resource consumption vulnerability in MELSEC iQ-R Series CPU Modules (R00/01/02CPU Firmware versions from '05' to '19' and R04/08/16/32/120(EN)CPU Firmware versions from '35' to '51') allows a remote attacker to cause an error in a CPU unit via a specially crafted HTTP packet, which may lead to a denial-of-service (DoS) condition in execution of the program and its communication.
How severe is CVE-2020-5666?: CVE-2020-5666 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2020-5666 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 8% (94th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2020-5666?: CVE-2020-5666 primarily affects Mitsubishielectric Melsec Iq-r00 Firmware. In total, 8 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2020-5666?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2020-5666 published?: CVE-2020-5666 was published on 2020-11-16 and last updated on 2026-06-17.

References

Affected products (8)

cpe:2.3:o:mitsubishielectric:melsec_iq-r00_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:mitsubishielectric:melsec_iq-r01_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:mitsubishielectric:melsec_iq-r02_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:mitsubishielectric:melsec_iq-r04_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:mitsubishielectric:melsec_iq-r16_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:mitsubishielectric:melsec_iq-r08_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:mitsubishielectric:melsec_iq-r32_firmware:*:*:*:*:*:*:*:*
cpe:2.3:o:mitsubishielectric:melsec_iq-r120_firmware:*:*:*:*:*:*:*:*

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