在Web App中公开AWS S3签名URL？

Question

I have been trying to find an answer to this question for a couple of hours now, but have not managed to come up with a conclusive answer. I am hoping someone here will be able to shed some light on my question. Consider the following Example AWS S3 URL:

https://some-bucket.s3-eu-west-2.amazonaws.com/uploads/images/some_image.jpg?X-Amz-Expires=600&X-Amz-Date=20170920T124015Z&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAI6CJYFYSSWMXXXXX/20170920/eu-west-2/s3/aws4_request&X-Amz-SignedHeaders=host&X-Amz-Signature=0481296b70633de9efb2fce6e20751df2f55fd79b5ff9570c02ff8f587dce825

In my specific example, the above URL is a request to view an image on S3 which I am exposing directly in a HTML img tag, and the user in Amz-Credential has both read and write permissions. The URL is also set to expire in 10 minutes.

Is is safe to link to the image directly via this URL, or is there any possibility that within these 10 minutes, the signature from this URL could be used in a maliciously crafted REST request to delete or modify the image instead of viewing it?

I do suspect a different action will have a different signature to make this impossible, but given my very limited understanding of AWS auth, I thought it better to ask just in case.

I know I could create a read-only user (extra complexity) or hide the S3 URL behind a controller action on my own web app (requires 2 total requests to load each image, making it inefficient), but I would rather learn whether my current approach is safe or not before resorting to either of these.

Thank you kindly for your time. :)

Answer 1

If your pre-signed url has PUT or DELETE permission someone could try to get the Signature + AccessKeyId to overwrite or delete your object.

Just make sure that you are signing the url with a read-only permission and I guess you're good.