HOMEVULNERABILITIESCVE-2021-20591
HIGH

CVE-2021-20591

CWE-400Published: June 11, 2021· Updated: Jun 17, 2026

7.5
CVSS v3.1

Official Description

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.

NVD Source

Technical Analysis

CVE-2021-20591 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in availability disruption (denial of service), with a CVSS base score of 7.5.

CVSS v3.1 Vector Breakdown

Exploitability
Attack VectorNetwork
Attack ComplexityLow
Privileges Req.None
User InteractionNone
ScopeUnchanged
Impact
ConfidentialityNone
IntegrityNone
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected Vendors & Products

mitsubishielectric40 product(s)
r00cpu firmwarer00cpur01cpu firmwarer01cpur02cpu firmwarer02cpur04cpu firmwarer04cpur08cpu firmwarer08cpur16cpu firmwarer16cpu+28
Source: NVD CPE · 40 total CPE entries

Exploit & PoC Resources

NO KNOWN EXPLOITNo public exploit confirmed at this time
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
External links open in a new tab. Always verify in a controlled environment before use.

Official Patches & Advisories

ADVISORYhttps://jvn.jp/vu/JVNVU98060539/index.html
ADVISORYhttps://www.mitsubishielectric.com/en/psirt/vulnerability/pdf/2021-003_en.pdf
ADVISORYhttps://jvn.jp/vu/JVNVU98060539/index.html
ADVISORYhttps://www.mitsubishielectric.com/en/psirt/vulnerability/pdf/2021-003_en.pdf

All References (4)

→
https://jvn.jp/vu/JVNVU98060539/index.htmlThird Party Advisory
→
https://www.mitsubishielectric.com/en/psirt/vulnerability/pdf/2021-003_en.pdfVendor Advisory
→
https://jvn.jp/vu/JVNVU98060539/index.htmlThird Party Advisory
→
https://www.mitsubishielectric.com/en/psirt/vulnerability/pdf/2021-003_en.pdfVendor Advisory

Quick Facts

CVE IDCVE-2021-20591
CVSS Score7.5 / 10
SeverityHIGH
WeaknessCWE-400
CISA KEVNo
Affected1 vendor(s)
PublishedJun 11, 2021

Related CVEs (CWE-400)

CVE-2023-30769
9.8
CVE-2017-9104
9.8
CVE-2019-2259
9.8
CVE-2023-28507
9.8
CVE-2015-4412
9.8
CVE-2025-24260
9.8

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-20591 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.
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