Amazon S3 Security and Access Management

To protect your data in Amazon S3, by default, users only have access to the S3 resources they create. You can grant access to other users by using one or a combination of the following access management features: AWS Identity and Access Management (IAM) to create users and manage their respective access; Access Control Lists (ACLs) to make individual objects accessible to authorized users; bucket policies to configure permissions for all objects within a single S3 bucket; and Query String Authentication to grant time-limited access to others with temporary URLs. Amazon S3 also supports Audit Logs that list the requests made against your S3 resources for complete visibility into who is accessing what data.

With a few clicks in the S3 management console, you can apply S3 Block Public Access to every bucket in your account—both existing and any new buckets created in the future—and make sure that there is no public access to any object. All new buckets have Block Public Access enabled by default. To restrict access to all existing buckets in your account, you can enable Block Public Access at the account level. S3 Block Public Access settings override S3 permissions that allow public access, making it easy for the account administrator to set up a centralized control to prevent variation in security configuration regardless of how an object is added or a bucket is created.

Amazon S3 Object Lock blocks object version deletion during a customer-defined retention period so that you can enforce retention policies as an added layer of data protection or for regulatory compliance. You can migrate workloads from existing write-once-read-many (WORM) systems into Amazon S3, and configure S3 Object Lock at the object- and bucket-levels to prevent object version deletions prior to pre-defined Retain Until Dates or Legal Hold Dates.

Amazon S3 Object Ownership disables Access Control Lists (ACLs), changing ownership for all objects to the bucket owner and simplifying access management for data stored in S3. When you configure the S3 Object Ownership Bucket owner enforced setting, ACLs will no longer affect permissions for your bucket and the objects in it. All access control will be defined using resource-based policies, user policies, or some combination of these. ACLs are automatically disabled for new buckets. You can use S3 Inventory to review ACLs usage in your buckets before enabling S3 Object Ownership when migrating to IAM-based buckets policies. For more information, see Controlling Object Ownership.

By default, all Amazon S3 resources—buckets, objects, and related subresources—are private: only the resource owner, an AWS account that created it, can access the resource. Amazon S3 offers access policy options broadly categorized as resource-based policies and user policies. You may choose to use resource-based policies, user policies, or some combination of these to manage permissions to your Amazon S3 resources. By default, an S3 object is owned by the account that created the object, including when this account is different than the bucket owner. You can use S3 Object Ownership to disable Access Control Lists and change this behavior. If you do, each object in a bucket is owned by the bucket owner. For more information, see Identity and access management in Amazon S3.

Discover and protect sensitive data at scale in Amazon S3 with Amazon Macie. Macie automatically provides you with a full inventory of your S3 buckets by scanning buckets to identify and categorize the data. You receive actionable security findings enumerating any data that fits these sensitive data types, including personal identifiable information (PII) (e.g. customer names and credit cards numbers), and categories defined by privacy regulations, such as GDPR and HIPAA. Macie also automatically and continually evaluates bucket-level preventative controls for any buckets that are unencrypted, publicly accessible, or shared with accounts outside of your organization, allowing you to quickly address unintended settings on buckets.

Amazon S3 automatically encrypts all object uploads to all buckets. For object uploads, Amazon S3 supports server-side encryption with four key management options: SSE-S3 (the base level of encryption), SSE-KMS, DSSE-KMS, and SSE-C, as well as client-side encryption. Amazon S3 offers flexible security features to block unauthorized users from accessing your data. Use VPC endpoints to connect to S3 resources from your Amazon Virtual Private Cloud (Amazon VPC). Use S3 Inventory to check the encryption status of your S3 objects  (see storage management for more information on S3 Inventory).

Video: Amazon S3 data encryption overview »

Trusted Advisor inspects your AWS environment and then makes recommendations when opportunities exist to help close security gaps. 

Trusted Advisor has the following Amazon S3-related checks: logging configuration of Amazon S3 buckets, security checks for Amazon S3 buckets that have open access permissions, and fault tolerance checks for Amazon S3 buckets that don't have versioning enabled, or have versioning suspended.

Access Amazon S3 directly as a private endpoint within your secure, virtual network with AWS PrivateLink for S3. Simplify your network architecture by connecting to S3 from on-premises or in the cloud using private IP addresses from your Virtual Private Cloud (VPC). You no longer need to use public IPs, configure firewall rules, or configure an internet gateway to access S3 from on-premises.

Choose from four supported checksum algorithms (SHA-1, SHA-256, CRC32, or CRC32C) to check data integrity on your upload and download requests. Automatically calculate and verify checksums as you store or retrieve data from Amazon S3, and access the checksum information at any time using the GetObjectAttributes S3 API or an S3 Inventory report.

S3 data integrity checking getting started tutorial

Tech Talk: Get started with checksums in Amazon S3 for data integrity checking

Blog: Building scalable checksums

Blog: Enabling and validating additional checksums on existing objects in Amazon S3