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How to enforce VPC endpoint policies in AWS?

Tags: Identity & access management Network security
tL;dr

Control AWS access via endpoint policies

A VPC endpoint policy allows you to control which AWS principals and actions are allowed through your private network connection to a service like S3. To enforce a VPC endpoint policy in AWS, attach a resource-based policy to the endpoint that explicitly allows or denies access to specific services, accounts, or actions. This is crucial for locking down access to AWS S3 buckets or other resources over a VPC endpoint and tightening your AWS security posture.

Sola lets you skip the mental gymnastics of stitching together IAM policies, bucket policies, and endpoint configs. Just write a prompt like “Who can access my S3 buckets via this VPC endpoint?” – and get the answer.
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Understand the VPC endpoint policy basics

When you create a VPC endpoint for S3, it feels private, but it is only as safe as its policies. If you leave the endpoint policy at its default, any principal in the VPC whose traffic routes through the endpoint and whose IAM permissions allow S3 actions can reach your buckets.

A custom endpoint policy lets you specify actions, resources, and principals, limiting who can use the endpoint. For example, you can allow only a specific IAM role to reach one bucket and deny everything else.

Just remember: the endpoint policy only governs traffic through the endpoint. If you haven’t locked down public access at the bucket level, users might still reach it over the internet. To block that, you’ll need conditions like aws:SourceVpce.

Remember that the endpoint policy governs traffic through the endpoint only. To stop users from reaching the same bucket over the public internet, add a bucket policy condition such as aws:SourceVpce (or aws:SourceVpc) so S3 accepts requests only from your endpoint.

Apply the same scrutiny elsewhere: verify RDS public access settings and secure AWS API Gateway with resource policies and private integrations to avoid parallel exposure paths.

Best Practices for Enforcing Endpoint Policies

  1. Use explicit denies for anything you absolutely want to block. IAM allows are permissive by default.
  2. Combine with S3 bucket policies to restrict access based on the aws:SourceVpce condition key. This ensures that even if a user has access, they must go through the intended VPC endpoint.
  3. Avoid overly broad permissions—limit access to exact actions (e.g. s3:GetObject) and specific resources.
  4. Test using IAM Policy Simulator or CloudTrail logs to validate that your endpoint policy behaves as expected.
  5. Tag your VPC endpoints and enforce tagging policies via SCPs or automation if you’re running multi-account setups.

Don’t just write it. Enforce it with Sola.

Want to know if your VPC endpoint policy is actually doing what you think it’s doing? Sola helps you find out in minutes. Use the AWS Network Security Posture app or build your own logic using Sola’s AI-powered studio. Just define your question (“Is any VPC endpoint letting in unwanted roles?”), connect your data source, and you’ve got an answer. No need for audits, spreadsheets, or assumptions.

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