The ISA/IEC 62443 series of standards is divided into four main parts, each covering a different aspect of industrial automation and control systems (IACS) cybersecurity1:
* Part 1: Terminology, Concepts, and Models
* Part 2: Policies and Procedures
* Part 3: System Requirements
* Part 4: Component Requirements The part 4 of the series focuses on the requirements for the secure development and maintenance of products that are used in IACS, such as controllers, sensors, actuators, network devices, software applications, and cloud services. The part 4 consists of two standards1:

Role-based access control (RBAC) is a method of restricting access to resources based on the roles of individual users within an organization. RBAC assigns permissions and responsibilities to roles, rather than to individual users, and then assigns users to those roles. This way, users can only perform the actions that are relevant and necessary for their role, and not access or modify any other resources that are beyond their scope of authority. RBAC is one of the security countermeasures that can be implemented in a defense-in-depth strategy, which is a layered approach to protect industrial automation and control systems (IACS) from cyber threats. RBAC can help prevent unauthorized access, misuse, or sabotage of IACS resources, as well as reduce the risk of human error or insider attacks.
References:
* ISA/IEC 62443-3-3:2013, Security for industrial automation and control systems - Part 3-3: System security requirements and security levels, Clause 5.3.2.11
* ISA/IEC 62443-2-1:2010, Security for industrial automation and control systems - Part 2-1: Establishing an industrial automation and control systems security program, Clause 6.2.2.32
* ISA/IEC 62443-4-1:2018, Security for industrial automation and control systems - Part 4-1: Product security development life-cycle requirements, Clause 5.2.3.23
* ISA/IEC 62443-4-2:2019, Security for industrial automation and control systems - Part 4-2: Technical security requirements for IACS components, Clause 4.2.3.24

The ISASecure Integrated Threat Analysis (ITA) Program is a certification scheme that certifies off-the-shelf automation and control systems to the ISA/IEC 62443 series of standards1. The ITA Program consists of three main components2:
* Software Development Security Assurance (SDSA): This component evaluates the security lifecycle and practices of the product supplier, such as security requirements, design, implementation, verification, and maintenance. The SDSA certification is based on the ISA/IEC 62443-4-1 standard.
* Functional Security Assessment (FSA): This component verifies the security functions and features implemented in the product, such as identification and authentication, access control, encryption, audit logging, and security management. The FSA certification is based on the ISA/IEC 62443-4-2 standard.
* Communications Robustness Testing (CRT): This component tests the resilience of the product against network attacks, such as denial-of-service, fuzzing, spoofing, and replay. The CRT certification is based on the ISA/IEC 62443-4-2 and ISA/IEC 62443-3-3 standards .
References:
* 1: ISASecure - IEC 62443 Conformance Certification - Official Site
* 2: ISASecure - IEC 62443 Conformance Certification - Official Site
* [3]: ISA/IEC 62443-4-1: Secure Product Development Lifecycle Requirements, ISA, 2018.
* [4]: ISA/IEC 62443-4-2: Technical Security Requirements for IACS Components, ISA, 2019.
* [5]: ISA/IEC 62443-4-2: Technical Security Requirements for IACS Components, ISA, 2019.
* [6]: ISA/IEC 62443-3-3: System Security Requirements and Security Levels, ISA, 2013.

Multiuser accounts and shared passwords are accounts and passwords that are used by more than one person to access a system or a resource. They inherently carry the risk of unauthorized access, which means that someone who is not authorized or intended to use the account or password can gain access to the system or resource, and potentially compromise its confidentiality, integrity, or availability. For example, if a multiuser account and password are shared among several operators of an industrial automation and control system (IACS), an attacker who obtains the password can use the account to access the IACS and perform malicious actions, such as changing the system settings, deleting data, or disrupting the process. Multiuser accounts and shared passwords also make it difficult to track and audit the activities of individual users, and to enforce the principle of least privilege, which states that users should only have the minimum level of access required to perform their tasks. Therefore, the ISA/IEC 62443 standards recommend avoiding the use of multiuser accounts and shared passwords, and instead using individual accounts and strong passwords for each user, and implementing authentication and authorization mechanisms to control the access to the IACS. References:
* ISA/IEC 62443-3-3:2013 - Security for industrial automation and control systems - Part 3-3: System security requirements and security levels1
* ISA/IEC 62443-2-1:2009 - Security for industrial automation and control systems - Part 2-1:
Establishing an industrial automation and control systems security program2
* ISA/IEC 62443 Cybersecurity Fundamentals Specialist Training Course3
Shared passwords and multiuser accounts pose specific risks, notably unauthorized access and privilege escalation. In ISA/IEC 62443's framework, these practices are discouraged because they complicate the attribution of actions to individual users and increase the likelihood that accounts can be used beyond their intended scope. Unauthorized access occurs when individuals exploit the shared nature of an account to gain entry to systems or data that they should not access. Privilege escalation can happen when users leverage shared accounts to perform actions at higher permission levels than those assigned to their personal accounts.
Conversely, buffer overflows and race conditions are types of vulnerabilities or programming errors, not directly associated with the risks of multiuser accounts or shared passwords.

According to the ISA/IEC 62443 standards, the level of risk an organization is willing to tolerate is determined by the management, as they are responsible for defining the business and risk objectives, as well as the security policies and procedures for the organization. The management also has the authority to allocate the necessary resources and assign the roles and responsibilities for implementing and maintaining the security program. The legal, operations, and safety departments may provide input and feedback to the management, but they do not have the final say in determining the risk tolerance level. References: ISA/IEC 62443-2-1:2010
- Establishing an industrial automation and control systems security program, section 4.2.1.