I want to use S3 to store user uploaded images. Some images like profile pictures and other thumbnails should be visible to anyone. However, I also want to have some images to be visible to users in the group that the image was "posted" to.
My app will handle all of the logic to decide whether or not a certain user has access to the image.
My question is: with a public S3 bucket and my app controlling the visibility of the images, how hard would it potentially be for someone to see images that they generally don't have access to?
Is there a better way to set up an S3 bucket to meet these requirements?
Thanks.
The best approach is:
Do not grant public access to any of the images/objects in Amazon S3
Your application at all times determines whether they should be allowed access
For users who are allowed access to an image, create an Amazon S3 Pre-Signed URL, which is a time-limited URL that will grant access to the object.
Your application can generate the pre-signed URL in a couple of lines of code, without requiring a call to AWS.
This way, all your security is maintained by the application rather than having to selectively make some objects public and there is no way for people to gain unauthorized access to objects.
Related
this might be a vague question but I am developing an app where users can upload files (mainly videos and pictures). Users can create groups and upload their images to the group and anyone in the group can view these files. I have the AWS S3 configured and working however, Aws recommends to keep the bucket Private.
if the bucket is private, is the only way to allow access for users to view content (maybe uploaded by friends VIA pre-signed urls?)
is it necessary to even make the bucket private. I see tutorials and they usually have the bucket settings to public. this means that any person that has a hold of the url can access an image. Lets say user 1 uploads to group xyz. only members of xyz should be able to access that image.
implementing unique identifiers for images will make it tough for someone to get access to that image but not impossible. would this be the better approach or having django generate signed URLS everytime a user wants to view a certain image? I feel like this is overkill for a photosharing app.
are there any other ways to add security?
Not necessarily buckets needs to be public. You can access the private files using url and keep it private. You may look at signature 4 security of s3. You can generate a url for files with params containing access keys with expiration time(key is different each time). Only having the access keys with the url private files are accessible. If the default ACL is private , DRF automatically adds the keys in the url.
This question is in the same line of thought than Is it possible to give token access to link to amazon s3 storage?.
Basically, we are building an app where groups of users can save pictures, that should be visible only to their own group.
We are thinking of using either a folder per user group, or it could even be an independent S3 bucket per user group.
The rules are very simple:
Any member of Group A should be able to add a picture to the Group A folder (or bucket)
Any member of Group A should be able to read all pictures of the Group A folder (or bucket)
No member of Group A should not have access to any of the pictures
However, the solution used by the post mentioned above (temporary pre-signed URLs) is not usable, as we need the client to be able to write files on his bucket as well as read the files on his bucket, without having any access to any other bucket. The file write part is the difficulty here and the reason why we cannot use pre-signed URLs.
Additionally, the solution from various AWS security posts that we read (for example https://aws.amazon.com/blogs/security/writing-iam-policies-grant-access-to-user-specific-folders-in-an-amazon-s3-bucket/) do not apply because they show how to control accesses for IAM groups of for other AWS accounts. In our case, a group of users does not have an IAM account...
The only solutions that we see so far are either insecure or wasteful
Open buckets to everybody and rely on obfuscating the folder / bucket names (lots of security issues, including the ability to brute force and read / overwrite anybody's files)
Have a back-end that acts as a facade between the app and S3, validating the accesses. S3 has no public access, the bucket is only opened to an IAM role that the back-end has. However this is a big waste of bandwidth, since all the data would transit on the EC2 instance(s) of that back-end
Any better solution?
Is this kind of customized access doable with S3?
The correct way to achieve your goal is to use Amazon S3 pre-signed URLs, which are time-limited URLs that provides temporary access to a private object.
You can also Upload objects using presigned URLs - Amazon Simple Storage Service.
The flow is basically:
Users authenticate to your back-end app
When a user wants to access a private object, the back-end verifies that they are permitted to access the object (using your own business logic, such as the Groups you mention). If they are allowed to access the object, the back-end generates a pre-signed URL.
The pre-signed URL is returned to the user's browser, such as putting it in a <img src="..."> tag.
When the user's browser requests the object, S3 verifies the signature in the pre-signed URL. If it is valid and the time period has not expired, S3 provides the requested object. (Otherwise, it returns Access Denied.)
A similar process is used when users upload objects:
Users authenticate to your back-end app
They request the opportunity to upload a file
Your back-end app generates an S3 Pre-signed URL that is included in the HTML page for upload
Your back-end should track the object in a database so it knows who performed the upload and keeps track of who is permitted to access the object (eg particular users or groups)
Your back-end app is fully responsible for deciding whether particular users can upload/download objects. It then hands-off the actual upload/download process to S3 via the pre-signed URLs. This reduces load on your server because all uploads/downloads go direct to/from S3.
I have upload all my images in s3 bucket and allowing it to show in my website using s3 url, but when I access the s3 url directly in browser it showing the image, I want to block those access
Can anyone help me on how to Block s3 public url access for my image and only show the image in mobile app or website.
All objects in Amazon S3 are private by default.
Access to objects can be granted in several ways:
A Bucket Policy can make a whole bucket (or a part of a bucket) public to everyone. It is also possible to specify restrictions, such as IP address and referer.
An Access Control List on an object can make the object public (for everyone)
An IAM Policy can grant access to objects for specific IAM Users
A pre-signed URL can provide temporary access to a private object
Based upon your question, I would recommend:
Keep the objects private (remove Bucket Policies and ACLs)
When a user wishes to access an image or other object, your application determines whether the user is permitted to access the object (this logic is totally up to you to write in your application)
If they are permitted, your application can create a pre-signed URL in a few lines of code, which will allow the mobile app or website to access the object for a limited time period that your app specifies (eg 5 minutes). After this time period, the URL will no longer provide access.
Thus, your application has full control over whether somebody is permitted to access the image, while still serving the content directly from Amazon S3 (eg in a web page via a <img> tag).
See: Share an Object with Others - Amazon Simple Storage Service
I am integrating the ability for users of my web app to be able to upload images to my site. I want to store these images in an AWS S3 bucket, but I need to be careful with privacy and making sure only people that should have access to these files can see them.
Users should have access to these files via <img src="s3_link"> but should not be able to access the bucket directly or list the objects within.
I can accomplish this by making the bucket public but this seems dangerous.
How do I set up a proper bucket policy to allow these images to be loaded onto a webpage in an <img> tag?
S3 supports pre-signed URLs. They can be used to restrict access to specific user.
See: Share an Object with Others
You might be able to use something like https://docs.aws.amazon.com/AmazonS3/latest/dev/example-bucket-policies.html#example-bucket-policies-use-case-4 (Restricting Access to a Specific HTTP Referrer).
It's going to be difficult to ensure complete control since S3 is a basic CND without the ability to create/grant permissions on the fly, coupled with the fact that you want your <img /> tags to grab the content directly from S3.
If you are trying to restrict downloads, you'll need to setup some basic logic to grant your users some type of access token that they will provide when requesting content to download (will require a lambda script/DB or a service that can pull the images down and then serve them if the caller is authenticated).
It sounds like you'll need authenticated users to request access to content via an API, passing in an Authorization token which the API will then verify if they have access to pull down the requested content.
I'm storing user images on S3 which are readable by default.
I need to access the images directly from the web as well.
However, I'd like to prevent hackers from brute forcing the URL and downloading my images.
For example, my S3 image url is at http://s3.aws.com/test.png
They can brute force test and download all the contents?
I cannot set the items inside my buckets to be private because I need to access directly from the web.
Any idea how to prevent it?
Using good security does not impact your ability to "access directly from the web". All content in Amazon S3 can be accessed from the web if appropriate permissions are used.
By default, all content in Amazon S3 is private.
Permissions to access content can then be assigned in several ways:
Directly on the object (eg make an object 'public')
Via a Bucket Policy (eg permit access to a subdirectory if accessed from a specific range of IP addresses, during a particular time of day, but only via HTTPS)
Via a policy assigned to an IAM User (which requires the user to authenticate when accessing Amazon S3)
Via a time-limited Pre-signed URL
The most interesting is the Pre-Signed URL. This is a calculated URL that permits access to an Amazon S3 object for a limited period of time. Applications can generate a Pre-signed URL and include the link in a web page (eg as part of a <img> tag). That way, your application determines whether a user is permitted to access an object and can limit the time duration that the link will work.
You should keep your content secure, and use Pre-signed URLs to allow access only for authorized visitors to your web site. You do have to write some code to make it work, but it's secure.