No exploitation reported

CVE-2021-20599

Q: Is CVE-2021-20599 actively exploited?

Active exploitation of CVE-2021-20599 has not been confirmed. Its EPSS score was 1.4% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-20599?

CVE-2021-20599 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.

No exploitation reported by the sources we read.

Published2021-10-14
WeaknessCWE-319 · CWE-639

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

Cleartext Transmission of Sensitive InformationCleartext transmission of sensitive information vulnerability in MELSEC iQ-R series Safety CPU R08/16/32/120SFCPU firmware versions "26" and prior and MELSEC iQ-R series SIL2 Process CPU R08/16/32/120PSFCPU firmware versions "11" and prior allows a remote unauthenticated attacker to login to a target CPU module by obtaining credentials other than password.

Timeline

dates in UTC

2021-10-1415:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-20599?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-20599?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

CISA-ADP · NVD

Mitsubishielectric melsec iq-r08sfcpu

Branch	Affected	Fixed in	Source
—	all versions	no fix published	CISA-ADP

Mitsubishielectric r08psfcpu

Branch	Affected	Fixed in	Source
—	all versions	no fix published	CISA-ADP

Mitsubishielectric r08psfcpu firmwareversion to verify

Branch	Affected	Fixed in	Source
—	all versions	no fix published	NVD

13 more products in the sources.

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

ICSA-21-287-03 CISA8 known affected
Mitsubishi Electric MELSEC iQ-R Series
Mitsubishi Electric Corporation MELSEC iQ-R series Safety CPU R08SFCPU Firmware: <=26 · Mitsubishi Electric Corporation MELSEC iQ-R series Safety CPU R16SFCPU Firmware: <=26 · Mitsubishi Electric Corporation MELSEC iQ-R series Safety CPU R32SFCPU Firmware: <=26 · +5 more

Full record on NVD

Fix

Mitigation from the vendor CISA ICSA-21-287-03 · 8 productsMitsubishi Electric has prepared the following countermeasures:
Mitigation from the vendor CISA ICSA-21-287-03 · 8 productsMELSEC iQ-R series Safety CPU R08/16/32/120SFCPU: Firmware versions "27" or later
Mitigation from the vendor CISA ICSA-21-287-03 · 8 productsMELSEC iQ-R series SIL2 Process CPU R08/16/32/120PSFCPU: Firmware versions "12" or later
Mitigation from the vendor CISA ICSA-21-287-03 · 8 productsCustomers using the affected products and versions may take measures through mitigations and workarounds. Mitsubishi Electric has released the fixed version as shown above, but updating the product to the fixed version is not available. Mitsubishi Electric recommends users take the following miti…
Mitigation from the vendor CISA ICSA-21-287-03 · 8 productsUse a firewall or virtual private network (VPN) to prevent unauthorized access when Internet access is required.
Mitigation from the vendor CISA ICSA-21-287-03 · 8 productsUse within a LAN and block access from untrusted networks and hosts through firewalls.

Advisories and patches

www.mitsubishielectric.comVendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

CISA-ADPSSVC decisionnone2024-04-22
OpenCVESSVC decisionnone—
CNACVSS 3.19.1read 2026-10-23
NVDCVSS 3.17.5read 2026-10-23
NVDCVSS 2.05read 2026-10-23
CNAweakness (CWE)CWE-319read 2026-10-23
NVDweakness (CWE)CWE-639read 2026-10-23
FIRST EPSSEPSS score1.4 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Published: 2021-10-14
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-20599?

Is CVE-2021-20599 actively exploited?

Active exploitation of CVE-2021-20599 has not been confirmed. Its EPSS score was 1.4% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-20599?

CVE-2021-20599 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.

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