How should a web application ensure security when serving confidential media files? - django

Question: Say a user uploads highly confidential information. This is placed in a third party storage server. This third party bucket uses different authentication systems to the web application. What is the best practice for ensuring only the user or an admin staff member can access the file url?
More Context: A Django web application is running on Google App Engine Flexible. Google Storage is used to serve static and media files through Django. The highly confidential information is passports, legal contracts etc.
Static files are served in a fairly insecure way. The /static/ bucket is public, and files are served through django's static files system. This works because
there is no confidential or user information in any of our static
files, only stock images, css and javascript, and
the files are uglified and minifed before production.
For media files however, we need user specific permissions, if user A uploads an image, then user A can view it, staff can view it, but user B & unauthenticated users cannot under any circumstances view it. This includes if they have the url.
My preferred system would be, that GCP storage could use the same django authentication server, and so when a browser requested ...google.storage..../media/user_1/verification/passport.png, we could check what permissions this user had, compare it against the uploaded user ID, and decide whether to show a 403 or the actual file.
What is the industry standard / best practice solution for this issue?
Do I make both buckets only accessible to the application, using a service account, and ensure internally that the links are only shared if the correct user is viewing the page? (anyone for static, and {user or staff} for media?)
My questions, specifically (regarding web application security):
Is it safe to serve static files from a publicly readable bucket?
Is it okay to assume that if my application requests a file url, that this is from an authenticated user?
Specifically with regards to Django & GCP Storage, if 2 is false (I believe it is) how do I ensure that files served from buckets are
only visible to users with the correct permissions?

Yes, it is. Public readable buckets are made for that. Things like, CSS, the logo of you company or some files that have no sensible data are safe to share.
Of course, do not use the same Public bucket to store private/public stuff. Public with Public, Private with Private.
Here is the problem. When you say "authenticated user", to whom you want that user to be authenticated to?
For example, if you authenticate your user using any Django methods, then the user will be authenticated to Django, but for Cloud Storage it will be an stranger. Also, even a user authorized on GCP may not be authorized to a bucket on Cloud Storage.
The important thing here is that the one that communicates back and forth with Cloud Storage is not the User, its Django. It could achieve this by using the python SDK of Cloud Storage, which takes the credentials of the service account that is being used on the instance to authenticate any request to Cloud Storage. So, the service account that is running the VM (because you are in Flexible) is the one that should be authorized to Cloud Storage.
You must first authorize the user on Django and then check if the User is able to access this file by other means(Like storing the name of the file he uploaded in a user_uploaded_files table).
Regarding your first question at the top of the post, Cloud Storage lets you create signed urls. This urls allow anyone on the internet to upload/download files from Cloud Storage by just holding the url. So you only need to authorize the user on Django to obtain the signed url and that's it. He does not need to be "authorized" on Cloud Storage(because the url already does it)
Taken from the docs linked before:
When should you use a signed URL?
In some scenarios, you might not
want to require your users to have a Google account in order to access
Cloud Storage, but you still want to control access using your
application-specific logic. The typical way to address this use case
is to provide a signed URL to a user, which gives the user read,
write, or delete access to that resource for a limited time. Anyone
who knows the URL can access the resource until the URL expires. You
specify the expiration time in the query string to be signed.

Following on from Nahuel Varela's answer:
My system now consists of 4 buckets:
static
media
static-staging
media-staging
Both the static buckets are public, and the media buckets are only accessible to the app engine service account created within the project.
(The settings are different for dev / test)
I'm using the django-storages[google]with #elnygrens modification. I modified this to remove the url method for Media (so that we create signed URLS) but keep it in for static (so that we access the public URL of the static files).
The authentication of each file access is done in Django, and if the user passes the test (is_staff or id matches file id), then they're given access to the file for a given amount of time (currently 1 hour), this access refreshes when the page loads etc.
Follow up question: What is the best practice for this time limit, I've heard people use anywhere from 15mins to 24 hours?

Related

Restrict all access to S3 static website except from our Elastic Beanstalk website

We have an Elastic Beanstalk instance that serves our PHP website (example.com). We just added an S3 bucket which serves a different static website (static.com).
The EB website (example.com) requires specific credentials which are supplied to the end-user for logging in. We would like to have the S3 website (static.com) only viewable to the logged-in users of the EB website (example.com) .
Use Cases:
A user is logged into “example.com”. Within the site there would be links to the files on “static.com”. Clicking on these links would take the user to the files on “static.com” and they could navigate around that site.
Someone has a URL to a page on “static.com”. Maybe someone shared that URL with them (that is expected behavior). When they attempt to load that URL in a browser, they are redirected to the login screen of “example.com” to login.
What is the best, and easiest, way to accomplish this? Cookies, Cloudfront, Lamda functions? “Signed URLs” sounded like a possible avenue, but the URLs cannot change over time. This is a requirement in case users do share the URLs (which is expected and ok). Example: Hey Johnny, check out the information at "static.com/docs/widget_1.html"
If you have private content, CloudFront signed URLs are the right choice to generate unique URLs for authenticated users of your application for a limited time. Each time a user loads a page, you generate new short-lived URLs.
If you'd like to enable someone to share links, one option is to provide users with a share option in your application that generates a SignedURL with a longer TTL of a fixed amount (e.g., 3 days) for sharing. Or enables the user to select the length of time the shareable link should be valid, with a maximum allowed time period of x hours/days. If the link expires, they can generate a new one in the application.

Selling access to web apps stored in S3 Bucket

I have several Rise 360 courses that I have exported to web apps and added them to my S3 bucket. I want to know the best was that I can sell access to these web apps from my website which I have built on the WordPress platform. I currently have 10 web apps in one bucket.
I don't want people to be able to take the URL and post it somewhere.
Content in Amazon S3 is private by default. Access is only available if you grant access in some way.
A good way to grant access to private content is to use Amazon S3 pre-signed URLs. These grant temporary access to private objects.
The flow would work something like this:
A user purchases a course
They then access a "My Courses" page
When generating that page, the PHP code would consult a database to determine what courses they have purchased
For each course they are allowed to access, the PHP code will generate a pre-signed URL to the course in Amazon S3. The URL can be configured to provide access for a period of time, such as 30 minutes
The user follows that URL and access the course. (Note: This assumes that only a single object is accessed.)
Once the expiry time is passed, the object is no longer accessible. The user would need to return to the "My Courses" page and click a newly-generated link to access the course again
If a user extracts the URL from the page, they will be able to download the object. You say "I don't want people to be able to take the URL and post it somewhere." This is not possible to guarantee because the app is granting them access to the object. However, that access will be time-limited so if they share the URL, it will stop working after a while.
If your app requires access to more than one URL (eg if the first page refers to a second page), then this method will not work. Instead, users will need to access the content via your app, with the app checking their access every time rather than allowing users to access the content directly from S3.

How to restrict users from download files uploaded to aws s3

I am developing a LMS in Laravel and uploading all the video files to aws s3 bucket and can play them using video js player. But problem is, users can download the video files, which I want to stop. Can anybody suggest me is it possible or not? If possible, can anyone tell me how can I do that?
Objects in Amazon S3 are private by default.
However, if you wish students to make use of a file (eg a learning course video), you will need to grant access to the file. The best way to do this is by using Amazon S3 pre-signed URLs, which provide time-limited access to a private object.
For example, the flow would be:
A students logs into the LMS
A student requests access to a course
The LMS checks whether they are entitled to view the course (using your own business logic)
If they are permitted to use the course, the LMS generates a pre-signed URL using a few lines of code, and returns the link in a web page (eg via an <a> tag).
The student can access the content
Once the expiry duration has passed, the pre-signed URL no longer works
However, during the period where the student has access to the file, they can download it. This is because access has been granted to the object. This is necessary because the web browser needs access to the object.
The only way to avoid this would be to provide courseware on a 'streaming' basis, where there is a continuous connection between the frontend and backend. This is not likely to be how your LMS is designed.

Secure image Urls

I am making a app that allows users to upload images to their profile page. I was using firebase Storage to store the images using a folder for each user. The problem I have is the Url for the images are accessible without evening signing into my app. Can I limit access to users that have signed in to my app? Im using a custom sign in token. Or do I need to switch to another storage provider.
It sounds like you're using Firebase Storage's download URLs. These are (by definition) URLs that give anyone who has them read-only access to the file. Download URLs are only generated when you call getDownloadUrl() (or the equivalent method on the platform you use). So if you don't want this behavior, don't call getDownloadUrl().
If you don't have a download URL, the files in Storage are only available by using the Firebase SDK. At that point all access to the files is secured through the security rules that you've defined for your project. For more on this, see the Firebase documentation on securing access to files.

Serve private, user-uploaded media from Google Cloud Storage

I'm evaluating using GCP for my new project, however, I'm still trying to figure out how to implement the following feature and what kind of costs it will have.
TL;DR
What's the best strategy to serve user-uploaded media from GCP while giving users full control on who will be able to access them?
Feature Description
As an User, I want to upload some kind of media (eg: image, videos, etc...) in a private and secure way.
The media must be visible by me and by a specific subgroup of users to which I've granted access to.
Anybody else must not be able to access the media, even if he obtained the URL.
The media content would then be displayed on the website.
Dilemma
I would like to use Cloud Storage to store all the media, however, I'm struggling to find a suitable solution for the authorization part.
As far as I can tell, features related to "Access Control" are mostly tailored at Project and Organisational level.
The closest feature so far are Signed URLs, but this doesn't satisfy the requirement of not being able to access it even if you have the URL, even though it expires soon after and perhaps it could be a good compromise.
Another problem with this approach is that the media cannot be cached at the browser level, which could save quite some bandwidth in the long run...
Expensive Solution?
One solution that came to my mind, is that I could serve it through a GCE instance by putting an App there that validate a user, probably through a JWT, and then stream it back while using the appropriate cache headers.
This should satisfy all requirements, but I'm afraid about egress costs skyrocketing :(
Thank you to whoever will help!
Signed URLs are the solution you want.
Create a service account that represents your application. When a user of your application wants to upload an object, vend them a signed URL for performing the upload. The new object will be readable only by your service account (and other members of your project).
When a user wants to view an object, perform whatever checks you like and then vend them a signed URL for reading the object. Set a short expiration time if you are worried about the URLs being shared.
I would not advise the GCE-based approach unless you get some additional benefit out of it. I don't see how it adds any additional security to serve the data directly instead of via a signed URL.