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🛡️ AWS EC2 Instance with an auto-assigned public IP address is in a default subnet🟢

  • Contextual name: 🛡️ Instance with an auto-assigned public IP address is in a default subnet🟢
  • ID: /ce/ca/aws/ec2/instance-with-public-ip-in-default-subnet
  • Tags:
  • Policy Type: COMPLIANCE_POLICY
  • Policy Categories: SECURITY, RELIABILITY

Logic​

Description​

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Description​

This policy checks if any AWS EC2 Instance with a public IP address is deployed within a default subnet.

By default, a default subnet is configured as a public subnet because the main route table is associated with an internet gateway, enabling outbound traffic to the internet.

Instances launched into a default subnet are automatically assigned a public IPv4 address, a private IPv4 address, and both public and private DNS hostnames.

Rationale​

Deploying instances in default subnets can inadvertently expose them to the public internet. Default VPCs and subnets are intended for ease of deployment and testing, rather than for building secure, production-grade environments.

Production workloads and sensitive resources should always be provisioned in custom VPCs with dedicated subnets, where routing, access, and security controls are explicitly defined and managed.

Audit​

This policy flags an AWS EC2 Instance as INCOMPLIANT if it has a Public IP Address and resides in a VPC Subnet where both Default For AZ and Map Public IP On Launch checkboxes are set to true.

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Remediation​

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Remediation​

From Command Line​

Consider two remediation paths:

  • Option 1: Remove the public IP address if it is not required.
  • Option 2: Relocate the instance to a purpose-built subnet (public or private, depending on requirements).
Option 1: Remove the Public IP Address​

If direct inbound access from the internet is not required, remove the public IP.

Modify network interface settings to disable public IP auto-assignment:

aws ec2 modify-network-interface-attribute \
    --network-interface-id {{network-interface-id}} \
    --no-associate-public-ip-address
aws ec2 modify-subnet-attribute \
    --subnet-id {{subnet-id}} \
    --no-map-public-ip-on-launch
Option 2: Move the Instance to a Custom Subnet​

If the instance must remain publicly accessible, it should be deployed in a custom public subnet with explicit security controls (e.g., restrictive security groups, NACLs).

If it only requires outbound internet access, deploy it into a private subnet that routes traffic through a NAT Gateway.

... see more

policy.yaml​

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Linked Framework Sections​

SectionSub SectionsInternal RulesPoliciesFlagsCompliance
💼 AWS Foundational Security Best Practices v1.0.0 → 💼 [EC2.9] Amazon EC2 instances should not have a public IPv4 address1no data
💼 Cloudaware Framework → 💼 Public and Anonymous Access113no data
💼 Cloudaware Framework → 💼 System Configuration55no data
💼 FedRAMP High Security Controls → 💼 AC-3 Access Enforcement (L)(M)(H)3779no data
💼 FedRAMP High Security Controls → 💼 AC-4 Information Flow Enforcement (M)(H)23796no data
💼 FedRAMP High Security Controls → 💼 AC-4(21) Physical or Logical Separation of Information Flows (M)(H)1156no data
💼 FedRAMP High Security Controls → 💼 AC-6 Least Privilege (M)(H)81170no data
💼 FedRAMP High Security Controls → 💼 AC-21 Information Sharing (M)(H)15no data
💼 FedRAMP High Security Controls → 💼 SC-7 Boundary Protection (L)(M)(H)10874no data
💼 FedRAMP High Security Controls → 💼 SC-7(3) Access Points (M)(H)15no data
💼 FedRAMP High Security Controls → 💼 SC-7(4) External Telecommunications Services (M)(H)42no data
💼 FedRAMP High Security Controls → 💼 SC-7(20) Dynamic Isolation and Segregation (H)15no data
💼 FedRAMP High Security Controls → 💼 SC-7(21) Isolation of System Components (H)31no data
💼 FedRAMP Low Security Controls → 💼 AC-3 Access Enforcement (L)(M)(H)79no data
💼 FedRAMP Low Security Controls → 💼 SC-7 Boundary Protection (L)(M)(H)43no data
💼 FedRAMP Moderate Security Controls → 💼 AC-3 Access Enforcement (L)(M)(H)79no data
💼 FedRAMP Moderate Security Controls → 💼 AC-4 Information Flow Enforcement (M)(H)180no data
💼 FedRAMP Moderate Security Controls → 💼 AC-4(21) Physical or Logical Separation of Information Flows (M)(H)56no data
💼 FedRAMP Moderate Security Controls → 💼 AC-6 Least Privilege (M)(H)670no data
💼 FedRAMP Moderate Security Controls → 💼 AC-21 Information Sharing (M)(H)15no data
💼 FedRAMP Moderate Security Controls → 💼 SC-7 Boundary Protection (L)(M)(H)760no data
💼 FedRAMP Moderate Security Controls → 💼 SC-7(3) Access Points (M)(H)15no data
💼 FedRAMP Moderate Security Controls → 💼 SC-7(4) External Telecommunications Services (M)(H)42no data
💼 NIST CSF v2.0 → 💼 DE.CM-01: Networks and network services are monitored to find potentially adverse events162no data
💼 NIST CSF v2.0 → 💼 DE.CM-09: Computing hardware and software, runtime environments, and their data are monitored to find potentially adverse events163no data
💼 NIST CSF v2.0 → 💼 ID.AM-03: Representations of the organization's authorized network communication and internal and external network data flows are maintained82no data
💼 NIST CSF v2.0 → 💼 PR.AA-05: Access permissions, entitlements, and authorizations are defined in a policy, managed, enforced, and reviewed, and incorporate the principles of least privilege and separation of duties127no data
💼 NIST CSF v2.0 → 💼 PR.DS-01: The confidentiality, integrity, and availability of data-at-rest are protected174no data
💼 NIST CSF v2.0 → 💼 PR.DS-02: The confidentiality, integrity, and availability of data-in-transit are protected150no data
💼 NIST CSF v2.0 → 💼 PR.DS-10: The confidentiality, integrity, and availability of data-in-use are protected170no data
💼 NIST CSF v2.0 → 💼 PR.IR-01: Networks and environments are protected from unauthorized logical access and usage113no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-3 Access Enforcement15552no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-3(7) Access Enforcement _ Role-based Access Control25no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-4 Information Flow Enforcement3269111no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-4(21) Information Flow Enforcement _ Physical or Logical Separation of Information Flows3756no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-6 Least Privilege102363no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-21 Information Sharing215no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7 Boundary Protection29481no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(3) Boundary Protection _ Access Points15no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(4) Boundary Protection _ External Telecommunications Services42no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(9) Boundary Protection _ Restrict Threatening Outgoing Communications Traffic26no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(11) Boundary Protection _ Restrict Incoming Communications Traffic31no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(16) Boundary Protection _ Prevent Discovery of System Components32no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(20) Boundary Protection _ Dynamic Isolation and Segregation15no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(21) Boundary Protection _ Isolation of System Components31no data