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AUSCERT External Security Bulletin Redistribution
Moxa Active OPC Server Unquoted Service Path Escalation Vulnerability
22 September 2016
AusCERT Security Bulletin Summary
Product: Moxa Active OPC Server
Operating System: Windows
Impact/Access: Execute Arbitrary Code/Commands -- Existing Account
Increased Privileges -- Existing Account
CVE Names: CVE-2016-5793
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Moxa Active OPC Server Unquoted Service Path Escalation Vulnerability
Original release date: September 20, 2016
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Independent researcher Zhou Yu has identified an unquoted service path
escalation vulnerability in Moxas 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,
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 PATH [a]
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.
CVE-2016-5793 [b] has been assigned to this vulnerability. A CVSS v3 base score
of 8.8 has been calculated; the CVSS vector string is
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
http://www.moxa.com/support (link is external).
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 ICSCERT 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
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,
web site last accessed September 20, 2016.
For any questions related to this report, please contact ICS-CERT at:
Email: firstname.lastname@example.org (link sends e-mail)
Toll Free: 1-877-776-7585
International Callers: (208) 526-0900
For industrial control systems security information and incident reporting:
ICS-CERT continuously strives to improve its products and services. You can
help by choosing one of the links below to provide feedback about this
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