S3 bucket object-level CloudTrail logging disabled

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Metadata

Id: a8fc2180-b3ac-4c93-bd0d-a55b974e4b07

Cloud Provider: AWS

Platform: Terraform

Severity: Medium

Category: Observability

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Description

S3 bucket object-level CloudTrail logging should be enabled for both read and write events by specifying read_write_type = "All" in the event_selector block. Without this, only management events are logged, leaving access or changes to individual objects unmonitored. If left unaddressed, this misconfiguration can result in undetected data exfiltration or unauthorized access, as malicious or accidental activities at the object level within the bucket would not be captured in CloudTrail logs.

Compliant Code Examples

data "aws_caller_identity" "current3" {}

resource "aws_cloudtrail" "example3" {
  name                          = "tf-trail-foobar"
  s3_bucket_name                = aws_s3_bucket.foo3.id
  s3_key_prefix                 = "prefix"
  include_global_service_events = false

  event_selector {
    read_write_type           = "All"
    include_management_events = true

    data_resource {
      type   = "AWS::S3::Object"
      values = ["arn:aws:s3:::"]
    }
  }
}

resource "aws_s3_bucket" "foo3" {
  bucket        = "tf-test-trail"
  force_destroy = true

  policy = <<POLICY
{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AWSCloudTrailAclCheck",
            "Effect": "Allow",
            "Principal": {
              "Service": "cloudtrail.amazonaws.com"
            },
            "Action": "s3:GetBucketAcl",
            "Resource": "arn:aws:s3:::tf-test-trail"
        },
        {
            "Sid": "AWSCloudTrailWrite",
            "Effect": "Allow",
            "Principal": {
              "Service": "cloudtrail.amazonaws.com"
            },
            "Action": "s3:PutObject",
            "Resource": "arn:aws:s3:::tf-test-trail/prefix/AWSLogs/${data.aws_caller_identity.current3.account_id}/*",
            "Condition": {
                "StringEquals": {
                    "s3:x-amz-acl": "bucket-owner-full-control"
                }
            }
        }
    ]
}
POLICY
}

Non-Compliant Code Examples

data "aws_caller_identity" "current2" {}

resource "aws_cloudtrail" "example2" {
  name                          = "tf-trail-foobar"
  s3_bucket_name                = aws_s3_bucket.foo2.id
  s3_key_prefix                 = "prefix"
  include_global_service_events = false

  event_selector {
    read_write_type           = "ReadOnly"
    include_management_events = true

    data_resource {
      type   = "AWS::S3::Object"
      values = ["arn:aws:s3:::"]
    }
  }
}

resource "aws_s3_bucket2" "foo" {
  bucket        = "tf-test-trail"
  force_destroy = true

  policy = <<POLICY
{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AWSCloudTrailAclCheck",
            "Effect": "Allow",
            "Principal": {
              "Service": "cloudtrail.amazonaws.com"
            },
            "Action": "s3:GetBucketAcl",
            "Resource": "arn:aws:s3:::tf-test-trail"
        },
        {
            "Sid": "AWSCloudTrailWrite",
            "Effect": "Allow",
            "Principal": {
              "Service": "cloudtrail.amazonaws.com"
            },
            "Action": "s3:PutObject",
            "Resource": "arn:aws:s3:::tf-test-trail/prefix/AWSLogs/${data.aws_caller_identity.current2.account_id}/*",
            "Condition": {
                "StringEquals": {
                    "s3:x-amz-acl": "bucket-owner-full-control"
                }
            }
        }
    ]
}
POLICY
}

data "aws_caller_identity" "current" {}

resource "aws_cloudtrail" "example" {
  name                          = "tf-trail-foobar"
  s3_bucket_name                = aws_s3_bucket.foo.id
  s3_key_prefix                 = "prefix"
  include_global_service_events = false

  event_selector {
    include_management_events = true

    data_resource {
      type   = "AWS::S3::Object"
      values = ["arn:aws:s3:::"]
    }
  }
}

resource "aws_s3_bucket" "foo" {
  bucket        = "tf-test-trail"
  force_destroy = true

  policy = <<POLICY
{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "AWSCloudTrailAclCheck",
            "Effect": "Allow",
            "Principal": {
              "Service": "cloudtrail.amazonaws.com"
            },
            "Action": "s3:GetBucketAcl",
            "Resource": "arn:aws:s3:::tf-test-trail"
        },
        {
            "Sid": "AWSCloudTrailWrite",
            "Effect": "Allow",
            "Principal": {
              "Service": "cloudtrail.amazonaws.com"
            },
            "Action": "s3:PutObject",
            "Resource": "arn:aws:s3:::tf-test-trail/prefix/AWSLogs/${data.aws_caller_identity.current.account_id}/*",
            "Condition": {
                "StringEquals": {
                    "s3:x-amz-acl": "bucket-owner-full-control"
                }
            }
        }
    ]
}
POLICY
}