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Debug an AWS S3 403 Access Denied Error

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Self-Hosting & Infra intermediate 8 min read $0.01 Updated 2026-10-19

Ordered checklist for S3 403 Access Denied errors: identify the caller with sts get-caller-identity, IAM and bucket policy evaluation, explicit denies, Block Public Access, KMS key permissions, object ownership, ACLs, VPC endpoints and cross-account access.

S3 returns AccessDenied or 403 even though the IAM policy looks right. Check which principal is calling, then bucket policy, block public access, KMS keys, object ownership and VPC endpoints in order.

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