OPC Foundation UA Products Built with .NET Framework

1. EXECUTIVE SUMMARY

• CVSS v3 7.5
• ATTENTION: Exploitable remotely/low attack complexity
• Vendor: OPC Foundation
• Equipment: OPC UA Servers
• Vulnerability: Uncontrolled Recursion

2. RISK EVALUATION

Successful exploitation of this vulnerability could trigger a stack overflow.

3. TECHNICAL DETAILS

3.1 AFFECTED PRODUCTS

The following OPC UA products are affected:

• OPC UA .NET Standard: versions prior to 1.4.365.48
• OPC UA .NET Legacy

3.2 VULNERABILITY OVERVIEW

3.2.1    UNCONTROLLED RECURSION CWE-674

The affected products are vulnerable to an uncontrolled recursion, which may allow an attacker to trigger a stack overflow.

CVE-2021-27432 has been assigned to this vulnerability. A CVSS v3 base score of 7.5 has been calculated; the CVSS vector string is (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

3.3 BACKGROUND

• CRITICAL INFRASTRUCTURE SECTORS: Multiple
• COUNTRIES/AREAS DEPLOYED: Worldwide
• COMPANY HEADQUARTERS LOCATION: United States

3.4 RESEARCHER

Eran Jacob with the Otorio Research Team reported this vulnerability to CISA.

4. MITIGATIONS

OPC Foundation recommends users install the OPC UA .NET Standard stack update.

CISA recommends 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 VPNs may have vulnerabilities and should be updated to the most current version available. Also recognize VPN is only as secure as its connected devices.

CISA reminds organizations to perform proper impact analysis and risk assessment prior to deploying defensive measures.



CISA also provides a section for control systems security recommended practices on the ICS webpage on us-cert.cisa.gov. 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 on the ICS webpage on us-cert.cisa.gov in the Technical Information Paper, ICS-TIP-12-146-01B--Targeted Cyber Intrusion Detection and Mitigation Strategies.



Organizations observing any suspected malicious activity should follow their established internal procedures and report their findings to CISA for tracking and correlation against other incidents.

No known public exploits specifically target this vulnerability.