Can aws s3 presigned urls be accessed by public?
Anyone with access to a presigned URL can use it to access the content it points to until the URL expires. Presigned URLs are generated by your server using your AWS credentials and grant temporary access to a private object in an S3 bucket. Because the access permission is embedded within the URL itself, including an expiration time, anyone who possesses the URL can access the object it references, without needing to authenticate or have direct access to the AWS account.
This is both a feature and a potential risk of using presigned URLs:
Feature:
- Secure Temporary Access: It allows you to give temporary access to private files stored in S3 without making them publicly accessible and without requiring users to have an AWS account or IAM permissions.
- Controlled Distribution: You can control who gets access by distributing these URLs to specific users under specific conditions (e.g., after a user has made a purchase).
Risk:
- Unauthorized Sharing: If a presigned URL is shared with others, those individuals can also access the content until the URL expires.
- Mitigation Strategies: To mitigate the risks associated with unauthorized sharing, consider the following strategies:
- Short Expiration Times: Use the shortest feasible expiration time for your use case. For example, if a video should only be accessible for a single viewing session, you might set the URL to expire in a few hours.
- Referer Header Checks: Implement checks for the HTTP referer header to ensure that requests for your content are coming from your application. This isn't foolproof, as headers can be spoofed, but it adds an additional layer of difficulty for unauthorized sharing.
- User-Specific Watermarking: For video content, embedding a user-specific watermark can deter users from sharing the content since any shared content can be traced back to them.
- Dynamic URL Regeneration: Regularly regenerate and update the presigned URLs for long-term access scenarios, and monitor access patterns for signs of abuse.
Implementation Considerations:
When implementing a system that uses presigned URLs, especially for sensitive or paid content, it's important to carefully consider the balance between user convenience and security. Adjusting the expiration time based on the content type and expected usage, and implementing additional security measures as needed, can help mitigate the risks associated with presigned URL sharing.