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AUSCERT External Security Bulletin Redistribution
Advisory (icsa-21-147-05) Mitsubishi Electric MELSEC iQ-R Series
28 May 2021
AusCERT Security Bulletin Summary
Product: MELSEC iQ-R Series Products
Operating System: Network Appliance
Impact/Access: Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2021-20591
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ICS Advisory (ICSA-21-147-05)
Mitsubishi Electric MELSEC iQ-R Series
Original release date: May 27, 2021
All information products included in https://us-cert.cisa.gov/ics are provided
"as is" for informational purposes only. The Department of Homeland Security
(DHS) does not provide any warranties of any kind regarding any information
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is governed by the Traffic Light Protocol (TLP) marking in the header. For more
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1. EXECUTIVE SUMMARY
o CVSS v3 5.3
o ATTENTION: Exploitable remotely/low attack complexity
o Vendor: Mitsubishi Electric
o Equipment: MELSEC iQ-R Series
o Vulnerability: Uncontrolled Resource Consumption
2. RISK EVALUATION
Successful exploitation of this vulnerability may prevent legitimate clients
from connecting to an affected product.
3. TECHNICAL DETAILS
3.1 AFFECTED PRODUCTS
The following MELSEC iQ-R series CPU modules are affected:
o R00/01/02CPU: All versions
o R04/08/16/32/120(EN)CPU: All versions
o R08/16/32/120SFCPU: All versions
o R08/16/32/120PCPU: All versions
o R08/16/32/120PSFCPU: All versions
3.2 VULNERABILITY OVERVIEW
3.2.1 UNCONTROLLED RESOURCE CONSUMPTION CWE-400
Due to improper session management, an attacker may prevent legitimate clients
from connecting to an affected product by manipulating the link parameter or
changing its state. If multiple MELSOFT transmission ports (TCP/IP) are open,
the other ports are not affected. Sequence control is not affected by this
CVE-2021-20591 has been assigned to this vulnerability. A CVSS v3 base score of
5.3 has been calculated; the CVSS vector string is ( AV:N/AC:L/PR:N/UI:N/S:U/
o CRITICAL INFRASTRUCTURE SECTORS: Critical Manufacturing
o COUNTRIES/AREAS DEPLOYED: Worldwide
o COMPANY HEADQUARTERS LOCATION: Japan
Younes Dragoni of Nozomi Networks reported this vulnerability to CISA.
Mitsubishi Electric recommends the following mitigations:
o Use a firewall, a virtual private network (VPN), etc., to prevent
unauthorized access when Internet access is required.
o Use within a LAN and block access from untrusted networks and hosts through
o Use the IP filter function to restrict the connectable IP addresses. See
MELSEC iQ-R Ethernet User's Manual (Application) 1.13 Security "IP filter"
for more information.
o Use the MELSOFT transmission port (UDP/IP).
o 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.
If this vulnerability is exploited, legitimate users can recover by first
disabling the port with the forced connection invalidation function and then
re-enabling the port. For an example see MELSEC iQ-R Ethernet User's Manual
(Application) Appendix 3, Buffer Memory.
Please refer to the Mitsubishi Electric advisory for further details.
CISA reminds organizations to perform proper impact analysis and risk
assessment prior to deploying defensive measures.
CISA also provides a section for control systems security recommended practices
on the ICS webpage on us-cert.cisa.gov . Several recommended practices are
available for reading and download, including Improving Industrial Control
Systems Cybersecurity with Defense-in-Depth Strategies .
Additional mitigation guidance and recommended practices are publicly available
on the ICS webpage on us-cert.cisa.gov in the Technical Information Paper,
ICS-TIP-12-146-01B--Targeted Cyber Intrusion Detection and Mitigation
Organizations observing any suspected malicious activity should follow their
established internal procedures and report their findings to CISA for tracking
and correlation against other incidents.
No known public exploits specifically target this vulnerability.
For any questions related to this report, please contact the CISA at:
Toll Free: 1-888-282-0870
CISA continuously strives to improve its products and services. You can help by
choosing one of the links below to provide feedback about this product.
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