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🛡️ AWS S3 Bucket ACL allows public read or write access🟢

Logic​

Similar Policies​

Description​

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Description​

This policy identifies AWS S3 Buckets that do not have Block Public ACLs enabled and whose Access Control List (ACLs) grants such public permissions as READ, WRITE, READ_ACP, WRITE_ACP, or FULL_CONTROL. Access is considered public if any of these permissions are granted to either the AllUsers group (anyone on the Internet) or the AuthenticatedUsers group (any AWS account holder).

Rationale​

Granting public access through ACLs poses a serious security risk. Public read access can lead to unintentional exposure of sensitive data, while public write access may allow unauthorized users to modify, delete, or upload objects. Such exposure can result in data breaches, service disruptions, or unexpected costs due to malicious uploads or misuse.

Audit​

This policy flags an AWS S3 Bucket as INCOMPLIANT if:

  • Block Public ACLs is not set to Yes, and
  • The Access Control Policy grants any of the following permissions: READ, WRITE, READ_ACP, WRITE_ACP, or FULL_CONTROL to either grantee:

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Remediation​

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Remediation​

Disable Public Access for S3 Bucket ACL​

Enable S3 Block Public Access​

Enabling Block Public Access provides a centralized and comprehensive mechanism to prevent public access to your S3 buckets. These settings override any existing ACLs or bucket policies that might otherwise allow public access.

From Command Line​

To enable Block Public Access on the bucket, run the following command:

aws s3api put-public-access-block \
    --bucket {{bucket-name}} \
    --public-access-block-configuration "BlockPublicAcls=true,IgnorePublicAcls=true,BlockPublicPolicy=true,RestrictPublicBuckets=true"
Apply the private Canned ACL​

Applying the private canned ACL removes all public access grants and ensures that only the bucket owner has full control.

aws s3api put-bucket-acl \
    --bucket {{bucket-name}} \
    --acl private

policy.yaml​

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Linked Framework Sections​

SectionSub SectionsInternal RulesPoliciesFlagsCompliance
💼 AWS Foundational Security Best Practices v1.0.0 → 💼 [S3.2] S3 general purpose buckets should block public read access2no data
💼 AWS Foundational Security Best Practices v1.0.0 → 💼 [S3.3] S3 general purpose buckets should block public write access2no data
💼 AWS Well-Architected → 💼 SEC08-BP04 Enforce access control7no data
💼 Cloudaware Framework → 💼 Public and Anonymous Access106no data
💼 FedRAMP High Security Controls → 💼 AC-3 Access Enforcement (L)(M)(H)3772no data
💼 FedRAMP High Security Controls → 💼 AC-4 Information Flow Enforcement (M)(H)23789no data
💼 FedRAMP High Security Controls → 💼 AC-4(21) Physical or Logical Separation of Information Flows (M)(H)1152no data
💼 FedRAMP High Security Controls → 💼 AC-6 Least Privilege (M)(H)81161no data
💼 FedRAMP High Security Controls → 💼 AC-21 Information Sharing (M)(H)12no data
💼 FedRAMP High Security Controls → 💼 SC-7 Boundary Protection (L)(M)(H)10864no data
💼 FedRAMP High Security Controls → 💼 SC-7(3) Access Points (M)(H)12no data
💼 FedRAMP High Security Controls → 💼 SC-7(4) External Telecommunications Services (M)(H)35no data
💼 FedRAMP High Security Controls → 💼 SC-7(20) Dynamic Isolation and Segregation (H)12no data
💼 FedRAMP High Security Controls → 💼 SC-7(21) Isolation of System Components (H)28no data
💼 FedRAMP Low Security Controls → 💼 AC-3 Access Enforcement (L)(M)(H)72no data
💼 FedRAMP Low Security Controls → 💼 SC-7 Boundary Protection (L)(M)(H)40no data
💼 FedRAMP Moderate Security Controls → 💼 AC-3 Access Enforcement (L)(M)(H)72no data
💼 FedRAMP Moderate Security Controls → 💼 AC-4 Information Flow Enforcement (M)(H)173no data
💼 FedRAMP Moderate Security Controls → 💼 AC-4(21) Physical or Logical Separation of Information Flows (M)(H)52no data
💼 FedRAMP Moderate Security Controls → 💼 AC-6 Least Privilege (M)(H)661no data
💼 FedRAMP Moderate Security Controls → 💼 AC-21 Information Sharing (M)(H)12no data
💼 FedRAMP Moderate Security Controls → 💼 SC-7 Boundary Protection (L)(M)(H)753no data
💼 FedRAMP Moderate Security Controls → 💼 SC-7(3) Access Points (M)(H)12no data
💼 FedRAMP Moderate Security Controls → 💼 SC-7(4) External Telecommunications Services (M)(H)35no data
💼 NIST CSF v2.0 → 💼 DE.CM-01: Networks and network services are monitored to find potentially adverse events150no data
💼 NIST CSF v2.0 → 💼 DE.CM-09: Computing hardware and software, runtime environments, and their data are monitored to find potentially adverse events149no data
💼 NIST CSF v2.0 → 💼 ID.AM-03: Representations of the organization's authorized network communication and internal and external network data flows are maintained76no 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 duties120no data
💼 NIST CSF v2.0 → 💼 PR.DS-01: The confidentiality, integrity, and availability of data-at-rest are protected164no data
💼 NIST CSF v2.0 → 💼 PR.DS-02: The confidentiality, integrity, and availability of data-in-transit are protected140no data
💼 NIST CSF v2.0 → 💼 PR.DS-10: The confidentiality, integrity, and availability of data-in-use are protected156no data
💼 NIST CSF v2.0 → 💼 PR.IR-01: Networks and environments are protected from unauthorized logical access and usage103no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-3 Access Enforcement15544no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-3(7) Access Enforcement _ Role-based Access Control18no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-4 Information Flow Enforcement326999no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-4(21) Information Flow Enforcement _ Physical or Logical Separation of Information Flows3752no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-6 Least Privilege102354no data
💼 NIST SP 800-53 Revision 5 → 💼 AC-21 Information Sharing212no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7 Boundary Protection29466no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(3) Boundary Protection _ Access Points12no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(4) Boundary Protection _ External Telecommunications Services35no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(9) Boundary Protection _ Restrict Threatening Outgoing Communications Traffic18no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(11) Boundary Protection _ Restrict Incoming Communications Traffic28no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(16) Boundary Protection _ Prevent Discovery of System Components29no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(20) Boundary Protection _ Dynamic Isolation and Segregation12no data
💼 NIST SP 800-53 Revision 5 → 💼 SC-7(21) Boundary Protection _ Isolation of System Components28no data
💼 PCI DSS v3.2.1 → 💼 1.2.1 Restrict inbound and outbound traffic to that which is necessary for the cardholder data environment, and specifically deny all other traffic.1060no data
💼 PCI DSS v3.2.1 → 💼 1.3.1 Implement a DMZ to limit inbound traffic to only system components that provide authorized publicly accessible services, protocols, and ports.624no data
💼 PCI DSS v3.2.1 → 💼 1.3.2 Limit inbound Internet traffic to IP addresses within the DMZ.24no data
💼 PCI DSS v3.2.1 → 💼 1.3.4 Do not allow unauthorized outbound traffic from the cardholder data environment to the Internet.11no data
💼 PCI DSS v3.2.1 → 💼 1.3.5 Permit only “established” connections into the network.24no data
💼 PCI DSS v3.2.1 → 💼 1.3.6 Place system components that store cardholder data in an internal network zone, segregated from the DMZ and other untrusted networks.11no data
💼 PCI DSS v3.2.1 → 💼 7.2.1 Coverage of all system components.10no data
💼 PCI DSS v4.0.1 → 💼 1.3.1 Inbound traffic to the CDE is restricted.60no data
💼 PCI DSS v4.0.1 → 💼 1.3.2 Outbound traffic from the CDE is restricted.60no data
💼 PCI DSS v4.0.1 → 💼 1.4.2 Inbound traffic from untrusted networks to trusted networks is restricted.24no data
💼 PCI DSS v4.0.1 → 💼 1.4.4 System components that store cardholder data are not directly accessible from untrusted networks.11no data
💼 PCI DSS v4.0.1 → 💼 7.3.1 An access control system(s) is in place that restricts access based on a user's need to know and covers all system components.10no data
💼 PCI DSS v4.0 → 💼 1.3.1 Inbound traffic to the CDE is restricted.760no data
💼 PCI DSS v4.0 → 💼 1.3.2 Outbound traffic from the CDE is restricted.60no data
💼 PCI DSS v4.0 → 💼 1.4.2 Inbound traffic from untrusted networks to trusted networks is restricted.724no data
💼 PCI DSS v4.0 → 💼 1.4.4 System components that store cardholder data are not directly accessible from untrusted networks.11no data
💼 PCI DSS v4.0 → 💼 7.3.1 An access control system(s) is in place that restricts access based on a user's need to know and covers all system components.10no data