S3 bucket should not be world-writable from anonymous users

Misconfigured S3 buckets can leak private information to the entire internet or allow unauthorized data tampering / deletion

Risk Level: Critical
Cloud Entity: Simple Storage Service (S3)
CloudGuard Rule ID: D9.AWS.IAM.30
Category: Storage


S3Bucket should not have acl.grants contain [uri = 'http://acs.amazonaws.com/groups/global/AuthenticatedUsers' and (premission = 'FULL_CONTROL' or premission = 'WRITE')]


From Portal:

  1. Go to Amazon S3 console
  2. Select the desired S3 bucket you want to change.
  3. Select the Permissions tab, and then go to Bucket Policy.
  4. Remove policies for s3:Put actions for principals ''. If necessary, modify the policy instead, to limit the access to specific principals.
    Then, select Access Control List, and remove any grants to Write objects to Public (everyone) users.

From TF:

resource "aws_s3_bucket" "test" {
	bucket = "mybucket"
	grant {
		type        = "Group"
		+   permissions = [...] #  not "WRITE" or "FULL_CONTROL" or "READ_ACP"
		uri         = "http://acs.amazonaws.com/groups/global/AuthenticatedUsers"

From Command Line:

  1. Get and put a bucket policy. The following example shows how to download an Amazon S3 bucket policy, make modifications to the file, and then use put-bucket-policy to apply the modified bucket policy. Run following command to download the bucket policy to a file.
aws s3api get-bucket-policy --bucket BUCKET_NAME --query Policy --output text > policy.json
  1. You can then modify the policy.json file as needed. Finally you can apply this modified policy back to the S3 bucket by running:
aws s3api put-bucket-policy --bucket BUCKET_NAME --policy POLICY.JSON

Note: Use action as s3:Put and Effect:Deny for user principals . Follow reference links for more details on json policy.


  1. https://docs.aws.amazon.com/AmazonS3/latest/dev/using-iam-policies.html
  2. https://docs.aws.amazon.com/AmazonS3/latest/userguide/access-policy-language-overview.html
  3. https://docs.aws.amazon.com/AmazonS3/latest/userguide/using-with-s3-actions.html
  4. https://docs.aws.amazon.com/cli/latest/reference/s3api/put-bucket-policy.html
  5. https://docs.aws.amazon.com/cli/latest/reference/s3api/get-bucket-policy.html

Simple Storage Service (S3)

Companies today need the ability to simply and securely collect, store, and analyze their data at a massive scale. Amazon S3 is object storage built to store and retrieve any amount of data from anywhere ��� web sites and mobile apps, corporate applications, and data from IoT sensors or devices. It is designed to deliver 99.999999999% durability, and stores data for millions of applications used by market leaders in every indu

Compliance Frameworks

  • AWS CCPA Framework
  • AWS CloudGuard Best Practices
  • AWS CloudGuard S3 Bucket Security
  • AWS CloudGuard SOC2 based on AICPA TSC 2017
  • AWS CloudGuard Well Architected Framework
  • AWS ISO 27001:2013
  • AWS ITSG-33
  • AWS LGPD regulation
  • AWS MAS TRM Framework
  • AWS MITRE ATT&CK Framework v10
  • AWS MITRE ATT&CK Framework v11
  • AWS NIST 800-171
  • AWS NIST 800-53 Rev 4
  • AWS NIST 800-53 Rev 5
  • AWS NIST CSF v1.1
  • AWS PCI-DSS 3.2
  • AWS Risk Management
  • AWS Security Risk Management