Mitsubishi Electric MELSEC-Q Series PLCs (Update B)
1. EXECUTIVE SUMMARY
- CVSS v3 7.5
- ATTENTION: Exploitable remotely/low skill level to exploit
- Vendor: Mitsubishi Electric
- Equipment: MELSEC-Q series PLCs
- Vulnerability: Resource Exhaustion
2. RISK EVALUATION
Successful exploitation of this vulnerability could allow a remote attacker to send specially crafted packets to the device via Ethernet, causing Ethernet and USB communication to stop.
3. TECHNICAL DETAILS
3.1 AFFECTED PRODUCTS
The following MELSEC-Q series PLCs are affected:
- Q03/04/06/13/26UDVCPU: serial number 20081 and prior
- Q04/06/13/26UDPVCPU: serial number 20081 and prior
- Q03UDECPU, Q04/06/10/13/20/26/50/100UDEHCPU: serial number 20101 and prior
3.2 VULNERABILITY OVERVIEW
3.2.1 UNCONTROLLED RESOURCE CONSUMPTION ('RESOURCE EXHAUSTION') CWE-400
A remote attacker can send specific packets over Ethernet to the affected products that will result in an Ethernet and USB communication crash.
CVE-2019-6535 has been assigned to this vulnerability. A CVSS v3 base score of 7.5 has been calculated; the CVSS vector string is (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
3.3 BACKGROUND
- CRITICAL INFRASTRUCTURE SECTORS: Critical Manufacturing
- COUNTRIES/AREAS DEPLOYED: Worldwide
- COMPANY HEADQUARTERS LOCATION: Japan
3.4 RESEARCHER
Tri Quach of Amazon's Customer Fulfillment Technology Security (CFTS) group reported this vulnerability to the National Cybersecurity and Communications Integration Center (NCCIC).
4. MITIGATIONS
Mitsubishi Electric has produced a new version of the firmware. Additional information about this vulnerability or Mitsubishi Electric's compensating control is available by contacting a local Mitsubishi Electric representative, which can be found at the following location: https://us.mitsubishielectric.com/fa/en/about-us/distributors
Mitsubishi Electric strongly recommends users should operate the affected device behind a firewall.
CISA recommends users take defensive measures to minimize the risk of exploitation of these vulnerabilities, such as:
- Minimize network exposure for all control system devices and/or systems, ensuring they are not accessible from the internet.
- Locate control system networks and remote devices behind firewalls and isolating them from business networks.
- When remote access is required, use more 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 the 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 cisa.gov/ics. Several CISA products detailing cyber defense best practices are available for reading and download, including Improving Industrial Control Systems Cybersecurity with Defense-in-Depth Strategies.
CISA encourages organizations to implement recommended cybersecurity strategies for proactive defense of ICS assets.
Additional mitigation guidance and recommended practices are publicly available on the ICS webpage at cisa.gov/ics in the technical information paper, ICS-TIP-12-146-01B--Targeted Cyber Intrusion Detection and Mitigation Strategies.
Organizations observing suspected malicious activity should follow established internal procedures and report findings to CISA for tracking and correlation against other incidents.
CISA also recommends users take the following measures to protect themselves from social engineering attacks:
- Do not click web links or open attachments in unsolicited email messages.
- Refer to Recognizing and Avoiding Email Scams for more information on avoiding email scams.
- Refer to Avoiding Social Engineering and Phishing Attacks for more information on social engineering attacks.
No known public exploitation specifically targeting this vulnerability has been reported to CISA at this time.
5. UPDATE HISTORY
- January 29, 2019: Initial Publication
- October 05, 2023: Update A - Updated vulnerability description
- June 24, 2025: Update B - Updated vulnerability description to include USB as an affected communication vector
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Vendor
- Mitsubishi Electric