I have created a "public Blob" container. Our application can add files to this container. The problem is everyone can see the files (PDF files) if they know the url and browe to them.
What can we do to prevent unauthorized users to see these files? Thanks
If you want to prevent unauthorized access you will need to change the container back to private. That way, only people with a valid account/key combination or people with a valid SAS can access the blobs.
The SAS can be used in different ways: by using it in the SDK (if you want your client applications to use it) or by appending it to the URL of the blob.
Check out Maarten's blog post about SAS to get started: Storing user uploads in Windows Azure blob storage
Access Control for Azure Blobs:
http://convective.wordpress.com/2010/01/20/access-control-for-azure-blobs/
Related
I have a few questions regarding firebase storage?
I am generating download URLs for firebase storage objects using and admin account (has custom claims) and storing the URL on Firestore.
Users can read the Firestore document to get the URL instead of having to call getDownloadUrl on the client side code.
Q1) I noticed there is a token at the end of the storage URLs. Is this specific to my admin account and is it safe that none admin users can now read this token?
Q2) Furthermore if a non admin user called getDownloadUrl on the same storage path would they receive the same URL as the admin account or a different one?
Q3) If I switch to using getDownloadUrl on the client side would this increase my cost when using firebase storage?
Q4) If i am caching the content by URL and the URL changes it will redownload and not use cache.. Are these download links unique or can getDownloadURL return different URLs on subsequent calls?
Thanks a lot
Edit ---
Sorry I have an additional question
Q5)To move files on firebase storage I currently download them to my local pc and reupload them to another location -- seems very inefficient.
I have seem people using file.move() (as can be seen here.)
Would this be possible to call in a firebase function (as they talk storage rules being an issue in the comments, although its from 2016) and if so how would this be cheaper than my manual download and upload?
Sorry for many questions :)
Q1) I noticed there is a token at the end of the storage URLs. Is this specific to my admin account and is it safe that none admin users can now read this token?
This token is a a random ID generated for this specific file. It won't change, unless you change it intentionally (you can "revoke" the token from the Firebase Console, which will replace it with a new token). Everyone who possesses the URL can view the file whether they are authenticated or not. However, the URL is "hard to guess", so unless you share it with anyone, it will stay secret, practically speaking.
Q2) Furthermore if a non admin user called getDownloadUrl on the same storage path would they receive the same URL as the admin account or a different one?
The returned URL will always be the same, unless you invalidate it in the Firebase Console. If you don't want clients to call getDownloadURL on the files, add a Storage Security Rule that denies reads:
match /path/to/{file} {
allow read: if false;
// Or, if only authed users should be able to call getDownloadURL:
allow read: if request.auth != null;
}
Q3) If I switch to using getDownloadUrl on the client side would this increase my cost when using firebase storage?
A call to getDownloadUrl() does utilize some Google Cloud resources that you will have to pay for, whether you do it server-side or client-side. It's a "Class B" operation (check Google Cloud pricing), and a bit of data transfer.
Q4) If i am caching the content by URL and the URL changes it will redownload and not use cache.. Are these download links unique or can getDownloadURL return different URLs on subsequent calls?
The same URL is return each time, unless you manually invalidate the token. (By the way, the caching policy that sets the Cache-Control header is set on the object as metadata when you upload it.)
Q5) To move files on firebase storage I currently download them to my local pc and reupload them to another location -- seems very inefficient. [..] Would this be possible to call in a firebase function
Yes, you can move files in a Firebase Cloud Function. The Firebase Admin SDKs bypasses security rules.
1) I noticed there is a token at the end of the storage URLs. Is this specific to my admin account and is it safe that none admin users can now read this token?
Depends on what you have at the moment since you can integrate Custom Authentication with Firebase which will allow you to create custom tokens that can be used to sign into the Firebase Authentication service on a client application and assume the identity described by the token’s claim. This can be used when accessing other Firebase services, such as Cloud Storage, etc.
In general your server should create a custom token with a unique identifier.
2) Furthermore if a non admin user called getDownloadUrl on the same storage path would they receive the same URL as the admin account or a different one?
Depends on how you are setting the permissions for the getDownloadUrl. If you have a customized one they can receive a different one but usually it returns a new instance that points to the current reference.
3) If I switch to using getDownloadUrl on the client side would this increase my cost when using firebase storage?
I am not sure about this, I have checked the documentation and there is nothing that would indicate a quota or pricing on this specific method so I would go ahead and assume that it would not do it but I might be wrong on this one.
4) If i am caching the content by URL and the URL changes it will redownload and not use cache.. Are these download links unique or can getDownloadURL return different URLs on subsequent calls?
As specified before, it returns a new instance that points to the current reference so these download links are unique.
5) To move files on firebase storage I currently download them to my local pc and reupload them to another location -- seems very inefficient.
For this question and the last part of your initial post I would suggest you to create a support ticket and ask more details to the Firebase Support Team where you can get more information regarding this since it is more suited for them than to StackOverflow. (https://firebase.google.com/support)
i have an Azure Blob Storage with blobs that are pdf that are categorized by client number. So for each client, they have multiple pdf reports. I only want the client to be able to access the blobs for their client number. (There are hundreds of clients.)
I've researched, but only see shared access signatures, but this doesn't look like what i need.
There is no user-level blob permissions, other than Shared Access Signatures (and Policies).
It's going to be up to you to manage access to specific user content (and how you manage that is really up to you and your app, and how you manage a user's content metadata).
When providing a link to a user's content: if you assume all content is always private, then simply create an on-demand SAS link when requested. There's no way for the user to modify a SAS link to guess sequential numbers or neighboring blobs, since the SAS is for a specific URL.
As Andrés suggested, you could also use your app to stream blob content, and never worry about SAS. However, you will now be consuming resources of your web app (network, CPU, memory), and this will have an impact on your app's scale requirements. You will no longer be able to offload this to the storage service.
Sounds like you already have the users authenticate, and you know which pdfs belong to them. My suggestion is to add to your current application a simple proxy (for instance if you have an MVC application, you could add a new controller and action method that will retrieve the pdfs on behalf of the user).
This way you don't need to use shared access signature and can keep the blob container private. Your controller/action method would simply use the storage SDK to retrieve the blob. An added bonus is that you could check to make sure that they are requesting their own PDF file and reject the request if they guess the ID of someone else's file.
Project ASP.NET
I will use Azure for my storage. Questions (requirements):
In my project I let my registered users download files. But I don't want the user to share this download link to unregistered people (example : the download link what I gave the registered user shall only be downloadable on their computer) .
I show only for registered users the download link, the registered users can download the files that I gave them
No one can delete my files
Question 1: This is really up to your app but... if you're giving direct links to blobs in Azure Storage, you would need to protect them with a Shared Access Signature (or policy). This way, you can give someone a link that expires (for example, 10 minutes after you issue the link). Then, if someone gives away the link, it won't work for very long. There's no way to limit a link's use to a specific computer. Now, if you simply stream content from blob to your app, and then from your app to the user, you will probably have a bit more control, since you wouldn't really be generating a reusable link. But this will have downsides (such as running all content through your web tier, requiring more resources in your web tier).
Question 2: This is completely up to your app, how you manage assets and present them to a registered user. No way to answer this for you, since we know nothing about your app.
Question 3: Azure Storage is accessible by a secret key, which should stay secret, and only you should ever have access to it (for example, it would be used by your code on the server). As long as you don't publish this key anywhere, then nobody would be able to delete your content.
Heres three questions for you!
Is it possible to revoke an active SAS URI without refreshing storage key or using Stored Access Policy?
In my application, all users share the same blob container. Because of this, using stored access policy, (max 5 per container), or refreshing storage key, (will result in ALL SAS URI'S being deleted), is not an option for me.
Is it possible to show custom errors if the SAS URI is incorrect or expired?
This is the default page:
If I let users create their own SAS URI for uploading/downloading, do I need to think about setting restrictions? Can this be abused?
Currently, in my application, there are restrictions on how much you are allowed to upload, but no restrictions on how many SAS URIS you are allowed to create. Users can aquire how many SAS URIS as they like as long as the don't complete their upload or exceed the allowed stored bytes.
How does real filesharing websites deal with this?
How much does a SAS URI cost to create?
Edit - Clarification of question 3.
Before you can upload or download a blob you must first get the SAS URI. I was wondering if it's "expensive" to create a SAS URI. Imagine a user exploiting this, creating a SAS URI over and over again without finishing the upload/download.
I was also wondering how real filesharing websites deal with this. It's easy to store information about how much storage the user is using and with that information put restrictions etc, but... If a user keeps uploading files to 99% and then cancel and restarts again and do the same thing, i imagine it would cost alot for the host
To answer your questions:
No, ad-hoc SAS tokens (i.e. tokens without Storage Access Policy) can't be revoked other than changing the storage key or access policy.
No, at this time it is not possible to customize error message. Standard error returned by storage service will be shown.
You need to provide more details regarding 3. As it stands, I don't think we have enough information to comment.
UPDATE
Regarding your question about how expensive creating a SAS URI is, one thing is that creating a SAS URI does not involve making a REST API call to storage service so there's no storage transaction involved. So from the storage side, there's no cost involved in creating a SAS URI. Assuming your service is a web application, only cost I could think of is user making call to your service to create a SAS URI.
Regarding your comment about how real file sharing websites deal with it, I think unless someone with a file sharing website answers it, it would be purely speculative.
(My Speculative response :)) If I were running a file sharing website, I would not worry too much about this kind of thing simply because folks don't have time to "mess around" with your site/application. It's not that the users would come to your website with an intention of "let's just upload files till the upload is 99%, cancel the upload and do that again" :). But again, it is purely a speculative response :).
I'm developing a filesharing website and I have a couple of questions regarding Windows Azure Shared Access Signatures.
About my website: Registered users can upload, share and store their files using blob storage. The files can be up to 2GB in size so I want the upload and download to be as fast as possible. It's
also important that the administartion cost for me as a host is at its minimum. User stored files must be private.
I'm OK with using SAS URI for uploads, but for downloads I'm abit spooked.
Questions:
1. Users can store files on their account and these files should only be accessed by that user. If I were to use SAS URI download here, the files will always be available with an URI as long as
the URI lives, (doesnt require you to be logged in if you know the URI, you can just download the file). This is quite scary if you want the file to be private. I know the signature in the SAS URI
is "HMAC computed over a string-to-sign and key using the SHA256 algorithm, and then encoded using Base64 encoding", is this safe? Is it acceptable to use SAS URI for downloads even if
the files are private? Should I instead stream the file between the server and website, (this will be much more safe but the speed will suffer and the administration cost will rise).
2. How much slower and how much more will it cost if I stream the downloads between (server, website, user) instead of using SAS, (server directly to user)?
3. If I set the SAS URI expiry time to 1 hour and the download takes longer than 1 hour, will the download cancel if the download started before the expiry time?
4. If my website is registered at x.azurewebsites.net and I'm using a purchased domain so I can access my website at www.x.com, is it possible to make the SAS URI's look somethinglike this:
https://x.com/blobpath instead of https://x.blob.core.windows.net/blobpath, (my guess is no..).
Sorry for the wall of text!
There's nothing that stops someone from sharing a URI, whether with or without a SAS. So from a safety perspective, if you leave the expiry date far-off into the future, the URI will remain accessible with the SAS-encoded URI. From an overall security perspective: Since your blob is private, nobody else will have access to the blob without a SAS-encoded URI. To limit SAS use: If, instead of being issued a long-standing SAS URI, the user visited a web page (or API) to request file access, you could generate a new SAS URI for a smaller time window; at this point, the end user would still be able to direct-access the blob without streaming the content through the VM (this just adds an extra network hop for obtaining the URI, along with whatever is needed to host the web / API server). Also related to security: If you use a stored access policy, you have the ability to modify access after issuing the SAS, rather than embedding start+end time directly into the SAS URI itself (see here info about access policies).
You'll incur the cost of the VM(s) used for fronting the URI requests. Outbound bandwidth costs are the same as using blob access directly: You pay for outbound bandwidth only. Performance will be affected by many things if going through a VM: VM size, VM resource use (e.g. if your VM is running at 100% CPU, you might see performance degredation), number of concurrent accesses, etc.
Yes, if the user hits expiry time, the link is no longer valid.
Yes, you can use a SAS combined with custom domain names used with storage. See here for more information about setting up custom domain names for storage.