Moxa Active OPC Server Unquoted Service Path Escalation Vulnerability
ICSA： ICS Advisory (ICSA-16-264-01)
Independent researcher Zhou Yu has identified an unquoted service path escalation vulnerability in Moxa’s Active OPC Server application. Moxa has produced a new version to mitigate this vulnerability. Zhou Yu has tested the new version to validate that it resolves the vulnerability.
Moxa reports that the vulnerability affects the following product:
- Active OPC Server versions older than Version 2.4.19
Successful exploitation of this vulnerability could potentially allow an authorized but nonprivileged local user to execute arbitrary code with elevated privileges on the system.
Impact to individual organizations depends on many factors that are unique to each organization. NCCIC/ICS-CERT recommends that organizations evaluate the impact of this vulnerability based on their operational environment, architecture, and product implementation.
Moxa is a Taiwan-based company that maintains offices in several countries around the world, including the US, UK, India, Germany, France, China, Russia, and Brazil.
The affected product, Active OPC Server, is a software package that operates as an OPC driver for an HMI or SCADA system. According to Moxa, Active OPC Server is deployed across several sectors including Commercial Facilities, Critical Manufacturing, Energy, Transportation Systems, and others. Moxa estimates that this product is used primarily in the United States and Europe with a small percentage in Asia.
UNQUOTED SERVICE PATHa
This vulnerability allows an authorized individual with access to a file system to possibly escalate privileges by inserting arbitrary code into the unquoted service path.
This vulnerability is not exploitable remotely and cannot be exploited without local authorized user credentials.
EXISTENCE OF EXPLOIT
No known public exploits specifically target this vulnerability.
An attacker with a low skill would be able to exploit this vulnerability.
Moxa recommends replacing existing Active OPC Server installations with the new software MX-AOPC UA server. Active OPC Server is nearing end of life by the end of 2016, and no further updates will be issued.
For existing Active OPC installations, Moxa suggests upgrading to Active OPC Server Version 2.4.19.
If more information about patching is needed, Moxa recommends contacting the Moxa Technical Support team or by visiting the Moxa technical support web page at:
ICS-CERT recommends that 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 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 reminds organizations to perform proper impact analysis and risk assessment prior to deploying defensive measures.
ICS-CERT also 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.
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 (http://ics-cert.us-cert.gov/).
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-428: Unquoted Search Path or Element, http://cwe.mitre.org/data/definitions/428.html, web site last accessed September 20, 2016.
- b. NVD, http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2016-5793, 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, https://www.first.org/cvss/calculator/3.0#CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H, web site last accessed September 20, 2016.