Framework № PCI DSS 4.0 от 01.03.2022

2.2.3 
Defined Approach Requirements: 
Primary functions requiring different security levels are managed as follows:

OR

OR

Customized Approach Objective:
Primary functions with lower security needs cannot affect the security of primary functions with higher security needs on the same system component. 
Defined Approach Testing Procedures:

Purpose:
Systems containing a combination of services, protocols, and daemons for their primary function will have a security profile appropriate to allow that function to operate effectively. For example, systems that need to be directly connected to the Internet would have a particular profile, like a DNS server, web server, or an e-commerce server. Conversely, other system components may operate a primary function comprising a different set of services, protocols, and daemons that performs functions that an entity does not want exposed to the Internet. This requirement aims to ensure that different functions do not impact the security profiles of other services in a way which may cause them to operate at a higher or lower security level. 

Good Practice:
Ideally, each function should be placed on different system components. This can be achieved by implementing only one primary function on each system component. Another option is to isolate primary functions on the same system component that have different security levels, for example, isolating web servers (which need to be directly connected to the Internet) from application and database servers. 
If a system component contains primary functions that need different security levels, a third option is to implement additional controls to ensure that the resultant security level of the primary function(s) with higher security needs is not reduced by the presence of the lower security primary functions. Additionally, the functions with a lower security level should be isolated and/or secured to ensure they cannot access or affect the resources of another system function, and do not introduce security weaknesses to other functions on the same server. 
Functions of differing security levels may be isolated by either physical or logical controls. For example, a database system should not also be hosting web services unless using controls like virtualization technologies to isolate and contain the functions into separate sub-systems. Another example is using virtual instances or providing dedicated memory access by system function. Where virtualization technologies are used, the security levels should be identified and managed for each virtual component. Examples of considerations for virtualized environments include: