Grant Access to AWS S3 bucket from specific IP without credentials - amazon-web-services

Question

I do not want to make my S3 bucket publicly accessible. But I expect it to be accessible from my local organization network without the AWS CLI or any credentials. How can I achieve it?.
I tried bucket policy with principal as * and source IP as the public IP of organization network.

Answer 1

If the intention is to grant anonymous access to a particular CIDR range, while also permitting IAM policies to grant additional access to specific people (eg Administrators), then this would not be appropriate.
IF you were to follow the initial example laid out by the AWS documentation - you’ll end up with a policy that probably looks similar to this.
{
"Id": "S3PolicyId1",
"Statement": [
{
"Sid": "IPAllow",
"Effect": "Allow",
"Principal": {
"AWS": "*"
},
"Action": "s3:*",
"Resource": "arn:aws:s3:::examplebucket/*",
"Condition": {
"IpAddress": {
"aws:SourceIp": "x.x.x.x/xx"
}
}
}
]
}
What you’re going to find, after banging your head on the table a few times, is that this policy does not work. There does not appear to be an implied deny rule with S3 buckets (similar to how IAM access policies are setup).
By default accounts are restricted from accessing S3 unless they have been given access via policy.
However, S3 is designed by default to allow any IP address access. So to block IP's you would have to specify denies explicitly in the policy instead of allows.
Once You learn this - the policy is easy to adjust. You just flipp around the policy from allowing access from only my IP address to denying access from everywhere that was NOT my IP address.
{
"Id": "S3PolicyId1",
"Statement": [
{
"Sid": "IPDeny",
"Effect": "Deny",
"Principal": {
"AWS": "*"
},
"Action": "s3:*",
"Resource": "arn:aws:s3:::examplebucket/*",
"Condition": {
"NotIpAddress": {
"aws:SourceIp": "xxx.x.x/xx"
}
}
}
] }
Hope this helps!

Answer 2

Yes, that is the correct way to do it.
From Bucket Policy Examples - Amazon Simple Storage Service:
{
"Version": "2012-10-17",
"Id": "S3PolicyId1",
"Statement": [
{
"Sid": "IPAllow",
"Effect": "Allow",
"Principal": "*",
"Action": "s3:GetObject",
"Resource": "arn:aws:s3:::examplebucket/*",
"Condition": {
"IpAddress": {"aws:SourceIp": "54.240.143.0/24"}
}
}
]
}