OPC Foundation UA .NET Standard versions prior to 1.4.365.48 and OPC UA .NET Legacy are vulnerable to an uncontrolled recursion, which may allow an attacker to trigger a stack overflow.

An issue was discovered in OPC UA .NET Standard Stack and Sample Code before GitHub commit 2018-04-12, and OPC UA .NET Legacy Stack and Sample Code before GitHub commit 2018-03-13. A vulnerability in OPC UA applications can allow a remote attacker to determine a Server's private key by sending carefully constructed bad UserIdentityTokens as part of an oracle attack.

An XXE vulnerability in the OPC UA Java and .NET Legacy Stack can allow remote attackers to trigger a denial of service.

Failure to validate certificates in OPC Foundation UA Client Applications communicating without security allows attackers with control over a piece of network infrastructure to decrypt passwords.

Unsigned versions of the DLLs distributed by the OPC Foundation may be replaced with malicious code.