CVE-2020-29457

Vulnerability

Overview

CVE-2020-29457 is a privilege elevation vulnerability in the OPC UA .NET Standard Stack, specifically in version 1.4.363.107. The root cause lies in improper certificate validation during the establishment of secure connections. The stack's certificate validation logic failed to properly reject invalid or untrusted certificates, allowing a rogue application to present a malicious certificate and be accepted as a legitimate peer [2]. This flaw enables an attacker to bypass authentication and establish a secure channel that should have been denied.

Exploitation

An attacker can exploit this vulnerability by deploying a rogue application that initiates a secure connection to an OPC UA server or client using the affected stack. No special network position is required beyond the ability to communicate with the target. The attacker does not need prior authentication; the vulnerability is triggered during the handshake phase when certificate validation is performed. The commit that addresses the issue (Pull Request #1229) shows changes to the Validate method, where additional error status codes (e.g., BadCertificateHostNameInvalid, BadCertificateUntrusted) are now properly handled to reject invalid certificates [2]. Prior to the fix, these errors were suppressed, allowing the connection to proceed.

Impact

Successful exploitation allows a rogue application to establish a secure OPC UA connection with elevated privileges. This could lead to unauthorized access to OPC UA data, commands, or configuration, potentially compromising the confidentiality, integrity, and availability of industrial control systems and other OPC UA-based applications. The vulnerability is classified as a privilege elevation issue because the attacker gains a level of trust that should not be granted.

Mitigation

The vulnerability is fixed in OPC UA .NET Standard Stack version 1.4.365 and later, as well as in the 1.5.x releases (e.g., 1.5.378.134) [1][2]. Users are strongly advised to update to the latest version of the OPCFoundation.NetStandard.Opc.Ua NuGet package. No workarounds are documented; updating the stack is the recommended mitigation. The vulnerability is listed on the NVD with a CVSS score (not provided here) and should be prioritized for patching in environments using the affected stack [4].