I created a Amazon S3 Bucket to store only images from my website. I have more than 1 million images all with public read access. Everytime I make a login, Amazon gives me this warning:
"This bucket has public access
You have provided public access to this bucket. We highly recommend that you never grant any kind of public access to your S3 bucket. "
I'm using the following Bucket Policy to only allow images to be shown just in my site:
{
"Version": "2012-10-17",
"Id": "http referer policy example",
"Statement": [
{
"Sid": "Allow get requests originated from www.example.com and example.com.br",
"Effect": "Allow",
"Principal": "*",
"Action": "s3:GetObject",
"Resource": "arn:aws:s3:::examplebucket.com/*",
"Condition": {
"StringLike": {
"aws:Referer": [
"http://www.example.com/*",
"http://www.example.com.br/*",
"https://www.example.com/*",
"https://www.example.com.br/*"
]
}
}
}
]
}
How can I revoke the public access to the bucket and to my files and grant it only to my sites?
Thank you!
It's a scary warning meant to prevent people from leaking data unintentionally. There have been lots of cases in the news lately about companies accidentally setting permissions to allow public reads.
In your case you really do want these to be publicly readable so you can just ignore the warning. Your security policy looks fine and still matches the documentation for public hosting.
You could theoretically put these images behind another server that streams them to the user if you really don't want someone to be able to download them directly. That's not really any more secure though.
If you do not want to have these publicly available at all just delete this policy from your bucket. In that case your website will not be able to serve the images.
Your policy looks good. You are providing a higher level of security then just public thru the referer header and not allowing the listing of objects.
Using S3 to provide common files such as CSS, JS and Images is just so easy. However, with all of the accidental security problems I usually recommend one of these approaches:
Turn on static web site hosting for the bucket. This makes it very clear to future admins that this bucket is intended for public files. Also I do not see big warning messages for these buckets. Enable redirect requests.
Better, turn off all public access and use CloudFront. Enable Origin Access Identity. You receive all the benefits of CloudFront, tighter security, etc.
Using an Origin Access Identity to Restrict Access to Your Amazon S3 Content
Related
I use S3 to stock static files for my website. Since my website has a login password, I would like to limit access to the static files on S3.
I successfully set the access permission like below.
{
"Version": "2012-10-17",
"Id": "http referer policy example",
"Statement": [
{
"Sid": "Allow get requests originating from www.example.com and example.com.",
"Effect": "Allow",
"Principal": "*",
"Action": "s3:GetObject",
"Resource": "arn:aws:s3:::mybucket/*",
"Condition": {
"StringLike": {
"aws:Referer": [
"https://mywebsite.com/*",
"http://127.0.0.1:8000/*"
]
}
}
}
]
}
And then, I tried to access the image directly by inputting the URL. I got the result(please see the attached).
My question:
Do you think it is safe to expose RequestID and HostID from a security perspective?
XML image. This is what I got
The Request ID and Host ID are identifiers within Amazon S3 that can be used for debugging and support purposes. There is no harm in S3 exposing that information, and you cannot prevent that information from appearing.
Also, please note that using aws:referer is a rather insecure method of protecting your content, since it can be easily spoofed (faked) when making a request to S3.
If you wish to protect valuable/confidential information in Amazon S3, then you should:
Keep all content in S3 as private (no bucket policy)
Users authenticate to your back-end app
When a user wants to access some private content from S3, your back-end app checks that they are entitled to access the content. If so, the back-end generates an Amazon S3 pre-signed URL, which is a time-limited URL that provides temporary access to a private object.
This can be provided as a direct link, or included in an HTML page (eg <img src="...">)
When S3 receives the pre-signed URL, it verifies the signature and checks the expiry time. If they are valid, it then returns the private object from the S3 bucket.
This way, you can use S3 to serve static content, but your application has full control over who is permitted to access the content. It cannot be faked like referer since each request is signed with a hash of the Secret Key.
I am hosting a website where users can write and read files, which are stored into another S3 Bucket. However, I want to restrict the access of these files only to my website.
For example, loading a picture.
If the request comes from my website (example.com), I want the read (or write if I upload a picture) request to be allowed by the AWS S3 storing bucket.
If the request comes from the user who directly writes the Object URL in his browser, I want the storing bucket to block it.
Right now, even with all I have tried, people can access ressources from the Object URL.
Here is my Bucket Policy:
{
"Version": "2012-10-17",
"Id": "Id",
"Statement": [
{
"Sid": "Sid",
"Effect": "Allow",
"Principal": "*",
"Action": [
"s3:PutObject",
"s3:GetObject",
"s3:GetObjectAcl"
],
"Resource": "arn:aws:s3:::storage-bucket/*",
"Condition": {
"StringLike": {
"aws:Referer": "http://example.com/*"
}
}
}
]
}
Additionnal informations:
All my "Block public access" are unchecked as you can see here. (I think that the problem comes from here. When I check the two boxes about ACL, my main problem is fixed, but I got a 403 error - Forbidden - when it comes to upload files to the Bucket, another problem);
My ACL looks like this;
My website is statically hosted on another S3 Bucket.
If you need more informations or details, ask me.
Thank you in advance for your answers.
This message has been written by a French speaking guy. Sorry for the mistakes
"aws:Referer": "http://example.com/*
The referer is an http header passed by the browser and any client could just freely set the value. It provides no real security
However, I want to restrict the access of these files only to my website
Default way restrict access to S3 resources for a website is using the pre-signed url. Basically your website backend can create an S3 url to download or upload an s3 object and pass the url only to authenticated /allowed client. Then your resource bucket can restrict the public access. Allowing upload without authentication is usually a very bad idea.
Yes, in this case your website is not static anymore and you need some backend logic to do so.
If your website clients are authenticated, you may use the AWS API Gateway and Lambda to create this pre-signed url for the clients.
I am trying to make sure I have my S3 bucket secure. I need to allow some sort of public access due to my website displays the images that are uploaded to my S3 bucket.
My Public Access settings look sleek this:
I then set up my Cross-origin resource sharing (CORS) to look like this:
[
{
"AllowedHeaders": [
"*"
],
"AllowedMethods": [
"GET",
"PUT",
"POST"
],
"AllowedOrigins": [
"https://example.com",
"https://www.example.com"
],
"ExposeHeaders": [],
"MaxAgeSeconds": 3000
}
]
And my S3 ACLs look like this:
After doing this my images are still visible on my website hosted on AWS. My question here is am I missing anything?
I don't think I fully understand the Cross-origin resource sharing (CORS) of this. I assumed the AllowedOrigins tag would only allow the images to be viewed on my domain? So I took the address to one of my images and threw it in my web browser and it loaded. Is this correct behavior or am I misunderstanding this?
Any more suggestions on how to secure my S3 bucket? I basically just want user on my website to be able to view my images and upload images from only my site. Thanks!
Updates
For a more full view, my bucket policy is:
{
"Version": "2008-10-17",
"Statement": [
{
"Sid": "AllowPublicRead",
"Effect": "Allow",
"Principal": {
"AWS": "*"
},
"Action": "s3:GetObject",
"Resource": "arn:aws:s3:::example.com.storage/*"
}
]
}
My ACLs in S3 are configured as:
You asked "how to secure my S3 bucket?"
Buckets in Amazon S3 are private by default, so they are automatically 'secure'. However, you want to make the objects (eg images) accessible to users on your website, so you need to open sufficient access to permit this (as you have successfully done!).
In fact, the only elements you actually needed were:
On "Block Public Access", allow Bucket Polices (Done!)
Create a Bucket Policy that grants GetObject to anyone (Done!)
You only need the CORS settings if you are experiencing a particular problem, and there is no need to change the Bucket ACLs from their default values.
The bucket policy is only allowing people to download objects, and only if they know the name of the object. They are not permitted to upload objects, delete objects or even list the objects in the bucket. That's pretty secure!
Your settings are fine for publicly-accessible content that you are happy for anyone to access. If you have any personal or confidential content (eg documents, or items requiring login) then you would need an alternate way of granting access only to appropriately authorized people. However, this doesn't seem to be a requirement in your situation.
Bottom line: You are correctly configured for granting public read-only access to anyone, without providing any additional access. Looks good!
Amazon CloudFront (CF) is often used for serving content from S3 buckets without needing the buckets to be public. This way your website would server your images from CF, rather than directly from the bucket. CF would fetch and cache the images from the bucket privately.
The way it works is that in your bucket, you would setup a special bucket policy which would allow a CF user, called origin access identity (OAI), to access your bucket.
The use of CF and OAI to serve your images from your bucket not only keeps your bucket fully private, but also reduces load times as CF caches the images in its edge locations.
More details on this are in:
Restricting Access to Amazon S3 Content by Using an Origin Access Identity
Amazon S3 + Amazon CloudFront: A Match Made in the Cloud
How do I use CloudFront to serve HTTPS requests for my Amazon S3 bucket?
I am trying to setup Cloudflare to cache images from S3. I want to be as restrictive (least permissive) as possible in doing this. I assume I need to accept requests from Cloudflare to read my S3 images. I want all other requests to be rejected.
I followed this guide: https://support.cloudflare.com/hc/en-us/articles/360037983412-Configuring-an-Amazon-Web-Services-static-site-to-use-Cloudflare
I did not enable static website hosting on my bucket, because it's not necessary for my case.
In my bucket permissions I turned off "Block all public access" and temporarily turned off "Block public access to buckets and objects granted through new public bucket or access point policies". I needed to do this in order to add a bucket policy.
From the link above, I then added a bucket policy that looks something like this:
{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "PublicReadGetObject",
"Effect": "Allow",
"Principal": "*",
"Action": "s3:GetObject",
"Resource": "arn:aws:s3:::www.example.com/*",
"Condition": {
"IpAddress": {
"aws:SourceIp": [
<CLOUDFLARE_IP_0>,
<CLOUDFLARE_IP_1>,
<CLOUDFLARE_IP_2>,
...
]
}
}
}
]
}
At this point, a message appeared in the AWS console stating:
"This bucket has public access
You have provided public access to this bucket. We highly recommend that you never grant any kind of public access to your S3 bucket."
I then turned back on "Block public access to buckets and objects granted through new public bucket or access point policies" and turned off "Block public and cross-account access to buckets and objects through any public bucket or access point policies".
At this point, the S3 image request behavior seems to be working as intended, but I am not confident that I set everything up to be minimally permissive, especially given the warning message in the AWS console.
Given my description, did I properly set things up in this bucket to accept read requests only from Cloudflare and deny all other requests? I want to make sure that requests from any origin other than Cloudflare will be denied.
Sounds good! If it works from CloudFlare, but not from somewhere else, then it meets your requirements.
Those Block Public Access warnings are intentionally scary to make people think twice before opening their buckets to the world.
Your policy is nicely limited to only GetObject and only to a limited range of IP addresses.
I have a static website created with Amazon S3. The only permissions I have set are through the bucket policy provided in Amazons tutorial:
{
"Version":"2012-10-17",
"Statement": [{
"Sid": "Allow Public Access to All Objects",
"Effect": "Allow",
"Principal": "*",
"Action": "s3:GetObject",
"Resource": "arn:aws:s3:::example.com/*"
}
]
}
Clearly, this policy enables the public to view any file stored on my bucket, which I want. My question is, is this policy alone enough to prevent other people from uploading files and/or hijacking my website? I wish for the public to be able to access any file on the bucket, but I want to be the only one with list, upload, and delete permissions. Is this the current behavior of my bucket, given that my bucket policy only addresses view permissions?
Have a look at this: http://docs.aws.amazon.com/IAM/latest/UserGuide/AccessPolicyLanguage_EvaluationLogic.html#policy-eval-basics
From that document:
When a request is made, the AWS service decides whether a given
request should be allowed or denied. The evaluation logic follows
these rules:
By default, all requests are denied. (In general, requests made using
the account credentials for resources in the account are always
allowed.)
An explicit allow overrides this default.
An explicit deny overrides any allows.
So as long as you don't explicitly allow other access you should be fine. I have a static site hosted on S3 and I have the same access policy.