ICS Advisory

IOServer Master Station Improper Input Validation

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Adam Crain of Automatak and independent researcher Chris Sistrunk have identified an improper input validation vulnerability in the IOServer DNP3 Driver on the master station. IOServer has produced a new version that mitigates this vulnerability. The researchers have tested the new version to validate that it resolves the vulnerability.

This vulnerability could be exploited remotely.


The following IOServer product versions are affected:

  • IOServer’s Beta2041.exe, and
  • IOServer’s versions older than driver19.exe.


The master station device can be put into an infinite loop by sending a specially crafted TCP packet, known as “TCP Connection Hijacking.” The device must be manually restarted to recover from the loop condition.

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.


IOServer is a New Zealand-based company that maintains users in several countries around the world, including the UK, Canada, New Zealand, Australia, Austria, France, Germany, Netherlands, Italy, India, Czech Republic, China, Singapore, South Korea, South Africa, and Brazil.

IOServer is a Windows-based (WindowsNT/95/98/ME/2000/2003/XP/2008/7) OPC Server that allows OPC clients such as human-machine interface and supervisory control and data acquisition systems to exchange plant floor data with programmable logic circuits. According to IOServer, the affected products are deployed across multiple sectors including manufacturing, building automation, oil and gas, water and wastewater, electric utilities, and others.



IMPROPER INPUT VALIDATIONCWE-20: Improper Input Validation  http://cwe.mitre.org/data/definitions/20.html, Web site last accessed August 01, 2013.

The IOServer driver does not validate or incorrectly validates input on the master server on Port 20000/TCP that can affect the control flow or data flow of a program. When this software does not validate input properly, an attacker is able to craft the input in a form that is not expected by the rest of the application. This will lead to parts of the system receiving unintended input, which may result in altered control flow or arbitrary control of a resource.

As a result, the IOServer enters an infinite loop condition without an exit. The system must then be restarted manually.

CVE-2013-2790NVD, http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2013-2790 , NIST uses this advisory to create the CVE Web site report. This Web site will be active sometime after publication of this advisory. has been assigned to this vulnerability. A CVSS v2 base score of 7.1 has been assigned; the CVSS vector string is (AV:N/AC:M/Au:N/C:N/I:N/A: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 August 01, 2013.



This vulnerability could be exploited remotely.


No known public exploits specifically target this vulnerability.


An attacker with a moderate skill would be able to exploit this vulnerability.


IOServer released Beta driver beta2042.exe resolves this vulnerability. This version has already been superseded by beta2043.exe. Information about this version of this product is available on the IOServer Web site:


The researchers suggest the following mitigation:

  • Block DNP3 traffic from traversing onto business or corporate networks through the use of an IPS or firewall with DPN3-specific rule sets.

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. Critical devices should not directly face 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 VPN is only as secure as the connected devices.

ICS-CERT also provides a section for control systems security recommended practices on the ICS-CERT Web page. Several recommended practices are available for reading and download, including Improving Industrial Control Systems Cybersecurity with Defense-in-Depth Strategies.CSSP Recommended Practices, http://ics-cert.us-cert.gov/content/recommended-practices, Web site last accessed August 01, 2013. ICS‑CERT reminds organizations to perform proper impact analysis and risk assessment prior to taking 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,Targeted Cyber Intrusion Detection and Mitigation Strategies, http://ics-cert.us-cert.gov/tips/ICS-TIP-12-146-01B, Web site last accessed August 01, 2013. that is available for download from the ICS-CERT Web page (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.

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