Top Server OPC Improper Input Validation Vulnerability

OVERVIEW

Adam Crain of Automatak and independent researcher Chris Sistrunk have identified an improper input validation vulnerability in the Software Toolbox TOP Server DNP Master OPC product. Software Toolbox 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.

AFFECTED PRODUCTS

The following Software Toolbox products are affected:

• DNP Master Driver for the TOP Server OPC Server (Version 5.11.250.0) and earlier.

IMPACT

The master station can be sent into an infinite loop by sending a specially crafted Transmission Control Protocol (TCP) packet or through serial communications. A successful attack exploiting this vulnerability could allow an attacker to put the master station into an infinite loop, causing a denial-of-service condition. The master station 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.

BACKGROUND

Software Toolbox is a US-based company that maintains offices primarily in North Carolina. The Software Toolbox TOP Server is used for industry and third-party connectivity communication software for automation, both OPC and embedded device communications.

The affected product is a Microsoft Windows-based software that facilitates connectivity to multiple DNP3 compliant devices such as human-machine interfaces, remote terminal units, programmable logic controllers, and meters. According to Software Toolbox, the TOP Server OPC I&C is deployed across several sectors including building automation, power distribution, oil and gas, and water and waste water.

VULNERABILITY CHARACTERIZATION

VULNERABILITY OVERVIEW

The Software Toolbox TOP Server DNP Master Driver does not validate input on Port 20000/TCP. This can allow an infinite loop to occur outside the protocol stack, requiring a manual restart to restore communication and control.

CVE-2013-2804NVD, http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2013-2804 , 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 visited August 22, 2013.

VULNERABILITY DETAILS

EXPLOITABILITY

This vulnerability could be exploited remotely.

EXISTANCE OF EXPLOIT

No known public exploits specifically target this vulnerability.

DIFFICULTY

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

MITIGATION

Software Toolbox has produced a new version of the software, Version 5.12.140.0, which resolves the vulnerability. This version was released June 18, 2013. Information and support about various versions are available at the Software Toolbox Top Server OPC I/O Server support site (registration required):
http://www.toolboxopc.com/html/v5_releasehistory.asp).

The most current version of TOP Server available is Version 5.12.142.0 R2 (issued August 5, 2013): http://www.toolboxopc.com/html/support.asp).

The researchers suggest the following mitigations:

• 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 22, 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 22, 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.

In addition, ICS‑CERT recommends that users take the following measures to protect themselves from social engineering attacks:

1. Do not click Web links or open unsolicited attachments in email messages.
2. Refer to Recognizing and Avoiding Email ScamsRecognizing and Avoiding Email Scams, http://www.us-cert.gov/reading_room/emailscams_0905.pdf, Web site last accessed August 22, 2013. for more information on avoiding email scams.

Refer to Avoiding Social Engineering and Phishing AttacksNational Cyber Alert System Cyber Security Tip ST04-014, http://www.us-cert.gov/cas/tips/ST04-014.html, Web site last accessed August 22, 2013. for more information on social engineering attacks.

• Software Toolbox