Ensure bucket ACL does not grant READ permission to AWS users

Error: Bucket ACL grants READ permission to AWS users

Bridgecrew Policy ID: BC_AWS_S3_6
Severity: CRITICAL

Bucket ACL grants READ permission to AWS users

Description

Unprotected S3 buckets are one of the major causes of data theft and intrusions. An S3 bucket that allows READ access to AWS Users can provide attackers the ability to read object data within the bucket, which can lead to the exposure of sensitive data. The only S3 buckets that should be globally accessible for unauthenticated users or for Any AWS Authenticate Users are those used for hosting static websites. Bucket ACL helps manage access to S3 bucket data.

We recommend AWS S3 buckets are not publicly accessible for READ actions to protect S3 data from unauthorized users and exposing sensitive data to public access.

Fix - Runtime

Procedure

S3 buckets should be protected by using the bucket ACL and bucket policies. If you want to share data with other users via S3 buckets, you could create pre-signed URLs with a short expiration duration.

To generate a pre-signed URL for the file samplefile.zip, use the following command:

aws s3 presign --expires-in 36000 s3://sharedfolder/samplefile.zip

To generate pre-signed URLS for every object in an S3 bucket, use the following command:

aws s3 ls --recursive s3://sharedfolder | awk '{print $4}' | 
while read line; do aws s3 presign --expires-in 36000 s3://sharedfolder/$line; done

📘

Note

For all automation-related work use the bucket policy and grant access to the required roles.

Fix - Buildtime

Terraform

  • Resource: aws_s3_bucket.data
  • Argument: acl
  • Repository: try-bridgecrew/terragoat
  • File Name: /terraform/s3.tf
    For example:
resource "aws_s3_bucket" "data" {
  # bucket is public
  # bucket is not encrypted
  # bucket does not have access logs
  # bucket does not have versioning
  bucket        = "${local.resource_prefix.value}-data"
  acl           = "public-read"
  force_destroy = true
  tags = {
    Name        = "${local.resource_prefix.value}-data"
    Environment = local.resource_prefix.value
  }
}

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