ICS Advisory (ICSA-21-182-04)

Mitsubishi Electric Air Conditioning System

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  • CVSS v3 7.1
  • ATTENTION: Exploitable remotely
  • Vendor: Mitsubishi Electric
  • Equipment: Multiple Air Conditioning Systems
  • Vulnerability: Incorrect Implementation of Authentication Algorithm


An attacker could exploit this vulnerability by impersonating administrators to disclose configuration information of the air conditioning system in order to tamper with operation information and system configuration.



Mitsubishi Electric reports this vulnerability affects the following air conditioning systems:

  • Air Conditioning System / Centralized Controllers affected:
    • G-50A: Version 2.50 to Version 3.35
    • GB-50A: Version 2.50 to Version 3.35
    • AG-150A-A: Versions 3.20 and prior
    • AG-150A-J: Versions 3.20 and prior
    • GB-50ADA-A: Versions 3.20 and prior
    • GB-50ADA-J: Versions 3.20 and prior
    • EB-50GU-A: Versions 7.09 and prior
    • EB-50GU-J: Versions 7.09 and prior
    • AE-200A: Versions 7.93 and prior
    • AE-200E: Versions 7.93 and prior
    • AE-50A: Versions 7.93 and prior
    • AE-50E: Versions 7.93 and prior
    • EW-50A: Versions 7.93 and prior
    • EW-50E: Versions 7.93 and prior
    • TE-200A: Versions 7.93 and prior
    • TE-50A: Versions 7.93 and prior
    • TW-50A: Versions 7.93 and prior
    • CMS-RMD-J: Versions 1.30 and prior
  • Air Conditioning System / Expansion Controllers are affected:
    • PAC-YG50ECA: Versions 2.20 and prior

To learn how to determine the version number of equipment, please see publication number 2021-004 from Mitsubishi Electric.



Web functions of Mitsubishi Electric air conditioning systems have a privilege escalation vulnerability due to incorrect implementation of the authentication algorithm. This vulnerability may allow an attacker to impersonate an administrator and tamper with information (e.g., operation information and configuration of the air conditioning system).

CVE-2021-20593 has been assigned to this vulnerability. A CVSS v3 base score of 7.1 has been assigned; the CVSS vector string is (AV:N/AC:H/PR:L/UI:N/S:C/C:L/I:H/A:N).




Chizuru Toyama of TXOne IoT/ICS Security Research Labs, working with Trend Micro’s Zero Day Initiative, reported this vulnerability to CISA.


Mitsubishi Electric has created the following versions to address the issue, and recommends users update to one of the following versions below or newer:

  • Air Conditioning System/Centralized Controllers:
    • G-50A: Version 3.37 or later
    • GB-50A: Version 3.37 or later
    • AG-150A-A: Version 3.21 or later
    • AG-150A-J: Version 3.21 or later
    • GB-50ADA-A: Version 3.21 or later
    • GB-50ADA-J: Version 3.21 or later
    • EB-50GU-A: Version 7.10 or later
    • EB-50GU-J: Version 7.10 or later
    • AE-200A: Version 7.95 or later
    • AE-200E: Version 7.95 or later
    • AE-50A: Version 7.95 or later
    • AE-50E: Version 7.95 or later
    • EW-50A: Version 7.95 or later
    • EW-50E: Version 7.95 or later
    • TE-200A: Version 7.95 or later
    • TE-50A: Version 7.95 or later
    • TW-50A: Version 7.95 or later
    • CMS-RMD-J: Version 1.40 or later
  • Air Conditioning System / Expansion Controllers:
    • PAC-YG50ECA: Version 2.21 or later

Mitsubishi Electric recommends users take the following mitigation measures to minimize the risks associated with this vulnerability:

  • Use a VPN router, etc. when connecting the air conditioning system to the Internet.
  • Use an antivirus software computer on systems used to connect conditioning systems.
  • Restrict the access to air conditioning systems from untrusted networks and hosts.
  • Change default usernames and passwords.

Please contact a distributor or Mitsubishi Electric representative for available updates. 

CISA recommends users take defensive measures to minimize the risk of exploitation of this vulnerability. Specifically, users should:

  • Minimize network exposure for all control system devices and/or systems, and ensure that they are not accessible from the Internet.
  • Locate control system networks and remote devices behind firewalls, and isolate them from the business network.
  • When remote access is required, use secure methods, such as Virtual Private Networks (VPNs), recognizing VPNs may have vulnerabilities and should be updated to the most current version available. Also recognize VPN is only as secure as its connected devices.

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 Strategies.

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. This vulnerability has a high attack complexity.

Contact Information

For any questions related to this report, please contact the CISA at:

Email: CISAservicedesk@cisa.dhs.gov
Toll Free: 1-888-282-0870

For industrial control systems cybersecurity information:  https://us-cert.cisa.gov/ics 
or incident reporting:  https://us-cert.cisa.gov/report

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