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Cloud Computing · Intermediate

S3 Bucket Policy

Resource-based JSON policy attached to an S3 bucket controlling which principals can perform which actions on it.

Definition

Bucket policies grant or deny access to a bucket and its objects for IAM principals, other accounts, services or anonymous users, with conditions such as source VPC endpoint, IP range or required TLS. They are commonly used for cross-account access and enforcing encryption in transit.

Example

A policy denies s3:* when aws:SecureTransport is false, forcing HTTPS.

Exam tip

For cross-account access, both the bucket policy and the requester's identity policy must allow the action; an explicit deny anywhere wins.

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