SC-21—Secure Name/address Resolution Service (recursive or Caching Resolver)

LI-SaaS

Low

Moderate

High

>Control Description

Request and perform data origin authentication and data integrity verification on the name/address resolution responses the system receives from authoritative sources.

>FedRAMP Baseline Requirements

Additional Requirements and Guidance

SC-21 Requirement: Control description should include how DNSSEC is implemented on recursive DNS servers to make DNSSEC requests when resolving DNS requests from internal components to domains external to the CSO boundary. - If the reply is signed, and fails DNSSEC, do not use the reply - If the reply is unsigned: -- CSP chooses the policy to apply SC-21 Requirement: Internal recursive DNS servers must be located inside an authorized environment. It is typically within the boundary, or leveraged from an underlying IaaS/PaaS. SC-21 Guidance: Accepting an unsigned reply is acceptable SC-21 Guidance: SC-21 applies to use of internal recursive DNS to access a domain outside the boundary by a component inside the boundary. - DNSSEC resolution to access a component inside the boundary is excluded.

>Discussion

Each client of name resolution services either performs this validation on its own or has authenticated channels to trusted validation providers. Systems that provide name and address resolution services for local clients include recursive resolving or caching domain name system (DNS) servers. DNS client resolvers either perform validation of DNSSEC signatures, or clients use authenticated channels to recursive resolvers that perform such validations.

Systems that use technologies other than the DNS to map between host and service names and network addresses provide some other means to enable clients to verify the authenticity and integrity of response data.

>Cross-Framework Mappings

SCF

NET-10.2

Compare

>Programmatic Queries

Beta

Related Services

Route 53 Resolver

VPC DNS

DNS Firewall

CLI Commands

List Route 53 Resolver endpoints

aws route53resolver list-resolver-endpoints --query 'ResolverEndpoints[*].{Id:Id,Name:Name,Direction:Direction,Status:Status}'

Check DNS Firewall rules

aws route53resolver list-firewall-rule-groups

List resolver rules

aws route53resolver list-resolver-rules --query 'ResolverRules[*].{Id:Id,Name:Name,RuleType:RuleType}'

Check DNSSEC validation

aws route53resolver list-resolver-dnssec-configs

Open AWS Console Documentation

>Assessment Interview Topics

Questions assessors commonly ask

Process & Governance:

•What policies govern the implementation of secure name/address resolution service (recursive or caching resolver)?
•How are system and communications protection requirements defined and maintained?
•Who is responsible for configuring and maintaining the security controls specified in SC-21?

Technical Implementation:

•How is secure name/address resolution service (recursive or caching resolver) technically implemented in your environment?
•What systems, tools, or configurations enforce this protection requirement?
•How do you ensure that secure name/address resolution service (recursive or caching resolver) remains effective as the system evolves?
•What network boundary protections are in place (firewalls, gateways, etc.)?

Evidence & Documentation:

•What documentation demonstrates the implementation of SC-21?
•Can you provide configuration evidence or system diagrams showing this protection control?
•What logs or monitoring data verify that this control is functioning correctly?
•Can you provide network architecture diagrams and firewall rulesets?

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