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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

Stats​

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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 → 💼 Network Exposure137no data
💼 Cloudaware Framework → 💼 System Configuration61no data
💼 FedRAMP High Security Controls → 💼 AC-3 Access Enforcement (L)(M)(H)49103no data
💼 FedRAMP High Security Controls → 💼 AC-4 Information Flow Enforcement (M)(H)248188no data
💼 FedRAMP High Security Controls → 💼 AC-4(21) Physical or Logical Separation of Information Flows (M)(H)18141no data
💼 FedRAMP High Security Controls → 💼 AC-6 Least Privilege (M)(H)81287no data
💼 FedRAMP High Security Controls → 💼 AC-21 Information Sharing (M)(H)19no data
💼 FedRAMP High Security Controls → 💼 SC-7 Boundary Protection (L)(M)(H)10999no data
💼 FedRAMP High Security Controls → 💼 SC-7(3) Access Points (M)(H)19no data
💼 FedRAMP High Security Controls → 💼 SC-7(4) External Telecommunications Services (M)(H)49no data
💼 FedRAMP High Security Controls → 💼 SC-7(20) Dynamic Isolation and Segregation (H)20no data
💼 FedRAMP High Security Controls → 💼 SC-7(21) Isolation of System Components (H)37no data
💼 FedRAMP Low Security Controls → 💼 AC-3 Access Enforcement (L)(M)(H)103no data
💼 FedRAMP Low Security Controls → 💼 SC-7 Boundary Protection (L)(M)(H)50no data
💼 FedRAMP Moderate Security Controls → 💼 AC-3 Access Enforcement (L)(M)(H)103no data
💼 FedRAMP Moderate Security Controls → 💼 AC-4 Information Flow Enforcement (M)(H)1169no data
💼 FedRAMP Moderate Security Controls → 💼 AC-4(21) Physical or Logical Separation of Information Flows (M)(H)141no data
💼 FedRAMP Moderate Security Controls → 💼 AC-6 Least Privilege (M)(H)687no data
💼 FedRAMP Moderate Security Controls → 💼 AC-21 Information Sharing (M)(H)19no data
💼 FedRAMP Moderate Security Controls → 💼 SC-7 Boundary Protection (L)(M)(H)783no data
💼 FedRAMP Moderate Security Controls → 💼 SC-7(3) Access Points (M)(H)19no data
💼 FedRAMP Moderate Security Controls → 💼 SC-7(4) External Telecommunications Services (M)(H)49no data
💼 NIST CSF v2.0 → 💼 DE.CM-01: Networks and network services are monitored to find potentially adverse events187no data
💼 NIST CSF v2.0 → 💼 DE.CM-09: Computing hardware and software, runtime environments, and their data are monitored to find potentially adverse events185no data
💼 NIST CSF v2.0 → 💼 ID.AM-03: Representations of the organization's authorized network communication and internal and external network data flows are maintained128no 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 duties199no data
💼 NIST CSF v2.0 → 💼 PR.DS-01: The confidentiality, integrity, and availability of data-at-rest are protected248no data
💼 NIST CSF v2.0 → 💼 PR.DS-02: The confidentiality, integrity, and availability of data-in-transit are protected219no data
💼 NIST CSF v2.0 → 💼 PR.DS-10: The confidentiality, integrity, and availability of data-in-use are protected249no data
💼 NIST CSF v2.0 → 💼 PR.IR-01: Networks and environments are protected from unauthorized logical access and usage165no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-3 Access Enforcement15866no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-3(7) Access Enforcement _ Role-based Access Control36no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-4 Information Flow Enforcement32120207no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-4(21) Information Flow Enforcement _ Physical or Logical Separation of Information Flows83141no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-6 Least Privilege102580no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-21 Information Sharing219no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7 Boundary Protection2911108no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(3) Boundary Protection _ Access Points19no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(4) Boundary Protection _ External Telecommunications Services49no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(9) Boundary Protection _ Restrict Threatening Outgoing Communications Traffic35no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(11) Boundary Protection _ Restrict Incoming Communications Traffic37no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(16) Boundary Protection _ Prevent Discovery of System Components37no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(20) Boundary Protection _ Dynamic Isolation and Segregation20no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(21) Boundary Protection _ Isolation of System Components37no data