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This advisory was originally posted to the US-CERT secure Portal library on May 26, 2015, and is being released to the NCCIC/ICS-CERT web site.
Ralf Spenneberg of OpenSource Security has identified a denial of service (DoS) vulnerability in the Mitsubishi Electric Automation, Inc., (Mitsubishi Electric) MELSEC FX-series controllers. Mitsubishi Electric has produced a new version that is not vulnerable to this issue.
This vulnerability could be exploited remotely.
The following MELSEC FX-series are affected:
- MELSEC FX3G Series PLCs.
A machine requires rebooting after this vulnerability has been exploited.
Impact to individual organizations depends on many factors that are unique to each organization. ICS-CERT recommends that organizations evaluate the impact of this vulnerability based on their operational environment, architecture, and product implementation.
Mitsubishi Electric is based in Vernon Hills, Illinois.
The affected products, MELSEC FX-series, are programmable logic controllers. According to Mitsubishi Electric, MELSEC FX-series controllers are deployed across several sectors including Commercial Facilities, Critical Manufacturing, Energy, Water and Wastewater Systems, and others. Mitsubishi Electric estimates that these products are used primarily in Asia with a small percentage in the United States and Europe.
IMPROPER HANDLING OF PARAMETERSa
The built-in HTTP application is unable to handle parameters that are longer than expected. A long parameter can cause a denial of service condition that requires a reboot to recover.
This vulnerability could be exploited remotely.
EXISTENCE OF EXPLOIT
No known public exploits specifically target this vulnerability.
An attacker with a medium skill would be able to exploit this vulnerability.
Mitsubishi Electric enhanced the MELSEC FX PLCs to prevent the DoS from occurring in new products starting in April 2015. They cannot guarantee the quality of new firmware in old hardware, so they do not plan to issue a firmware upgrade to existing customers.
ICS-CERT encourages asset owners to take additional defensive measures to protect against this and other cybersecurity risks.
- 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 that VPNs may have vulnerabilities and should be updated to the most current version available. Also recognize that VPN is only as secure as the connected devices.
ICS-CERT provides a section for control systems security recommended practices on the ICS‑CERT web page at http://ics-cert.us-cert.gov/content/recommended-practices. Several recommended practices are available for reading and download, including Improving Industrial Control Systems Cybersecurity with Defense-in-Depth Strategies. ICS-CERT reminds organizations to perform proper impact analysis and risk assessment prior to deploying defensive measures.
Additional mitigation guidance and recommended practices are publicly available in the ICS‑CERT Technical Information Paper, ICS-TIP-12-146-01B—Targeted Cyber Intrusion Detection and Mitigation Strategies, that is available for download from the ICS-CERT web site (www.ics-cert.org).
Organizations observing any suspected malicious activity should follow their established internal procedures and report their findings to ICS-CERT for tracking and correlation against other incidents.
- a. CWE-233: Improper Handling of Parameters, http://cwe.mitre.org/data/definitions/233.html, web site last accessed May 26, 2015.
- b. NVD, http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2015-3938, NIST uses this advisory to create the CVE web site report. This web site will be active sometime after publication of this advisory.
- c. CVSS Calculator, http://nvd.nist.gov/cvss.cfm?version=2&vector=AV:N/AC:M/Au:N/C:N/I:N/A:C , web site last accessed May 26, 2015.
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