KMS Allows Wildcard Principal

• Query id: f6049677-ec4a-43af-8779-5190b6d03cba
• Query name: KMS Allows Wildcard Principal
• Platform: CloudFormation
• Severity: Medium
• Category: Access Control
• CWE: 284
• URL: Github

Description

KMS Should not allow Principal parameter to be set as *
Documentation

Code samples

Code samples with security vulnerabilities

Positive test num. 1 - yaml file

AWSTemplateFormatVersion: 2010-09-09
Description: A sample template
Resources:
  myKey:
    Type: AWS::KMS::Key
    Properties:
      Description: An example symmetric CMK
      KeyPolicy:
        Version: '2012-10-17'
        Id: key-default-1
        Statement:
        - Sid: Enable IAM User Permissions
          Effect: Allow
          Principal: "*"
          Action: kms:*
          Resource: '*'
        - Sid: Allow administration of the key
          Effect: Allow
          Principal:
            AWS: arn:aws:iam::123456789012:user/Alice
          Action:
          - kms:Create*
          - kms:Describe*
          - kms:Enable*
          - kms:List*
          - kms:Put*
          - kms:Update*
          - kms:Revoke*
          - kms:Disable*
          - kms:Get*
          - kms:Delete*
          - kms:ScheduleKeyDeletion
          - kms:CancelKeyDeletion
          Resource: '*'
        - Sid: Allow use of the key
          Effect: Allow
          Principal:
            AWS: arn:aws:iam::123456789012:user/Bob
          Action:
          - kms:DescribeKey
          - kms:Encrypt
          - kms:Decrypt
          - kms:ReEncrypt*
          - kms:GenerateDataKey
          - kms:GenerateDataKeyWithoutPlaintext
          Resource: '*'

Positive test num. 2 - json file

{
  "AWSTemplateFormatVersion": "2010-09-09T00:00:00Z",
  "Description": "A sample template",
  "Resources": {
    "myKey": {
      "Properties": {
        "Description": "An example symmetric CMK",
        "KeyPolicy": {
          "Version": "2012-10-17",
          "Id": "key-default-1",
          "Statement": [
            {
              "Resource": "*",
              "Sid": "Enable IAM User Permissions",
              "Effect": "Allow",
              "Principal": "*",
              "Action": "kms:*"
            },
            {
              "Sid": "Allow administration of the key",
              "Effect": "Allow",
              "Principal": {
                "AWS": "arn:aws:iam::123456789012:user/Alice"
              },
              "Action": [
                "kms:Create*",
                "kms:Describe*",
                "kms:Enable*",
                "kms:List*",
                "kms:Put*",
                "kms:Update*",
                "kms:Revoke*",
                "kms:Disable*",
                "kms:Get*",
                "kms:Delete*",
                "kms:ScheduleKeyDeletion",
                "kms:CancelKeyDeletion"
              ],
              "Resource": "*"
            },
            {
              "Sid": "Allow use of the key",
              "Effect": "Allow",
              "Principal": {
                "AWS": "arn:aws:iam::123456789012:user/Bob"
              },
              "Action": [
                "kms:DescribeKey",
                "kms:Encrypt",
                "kms:Decrypt",
                "kms:ReEncrypt*",
                "kms:GenerateDataKey",
                "kms:GenerateDataKeyWithoutPlaintext"
              ],
              "Resource": "*"
            }
          ]
        }
      },
      "Type": "AWS::KMS::Key"
    }
  }
}

Code samples without security vulnerabilities

Negative test num. 1 - yaml file

AWSTemplateFormatVersion: 2010-09-09
Description: A sample template
Resources:
  myKey:
    Type: AWS::KMS::Key
    Properties:
      Description: An example symmetric CMK
      KeyPolicy:
        Version: '2012-10-17'
        Id: key-default-1
        Statement:
        - Sid: Enable IAM User Permissions
          Effect: Allow
          Principal:
            AWS: arn:aws:iam::111122223333:root
          Action: kms:*
          Resource: '*'
        - Sid: Allow administration of the key
          Effect: Allow
          Principal:
            AWS: arn:aws:iam::123456789012:user/Alice
          Action:
          - kms:Create*
          - kms:Describe*
          - kms:Enable*
          - kms:List*
          - kms:Put*
          - kms:Update*
          - kms:Revoke*
          - kms:Disable*
          - kms:Get*
          - kms:Delete*
          - kms:ScheduleKeyDeletion
          - kms:CancelKeyDeletion
          Resource: '*'
        - Sid: Allow use of the key
          Effect: Allow
          Principal:
            AWS: arn:aws:iam::123456789012:user/Bob
          Action:
          - kms:DescribeKey
          - kms:Encrypt
          - kms:Decrypt
          - kms:ReEncrypt*
          - kms:GenerateDataKey
          - kms:GenerateDataKeyWithoutPlaintext
          Resource: '*'

Negative test num. 2 - json file

{
  "AWSTemplateFormatVersion": "2010-09-09T00:00:00Z",
  "Description": "A sample template",
  "Resources": {
    "myKey": {
      "Type": "AWS::KMS::Key",
      "Properties": {
        "Description": "An example symmetric CMK",
        "KeyPolicy": {
          "Version": "2012-10-17",
          "Id": "key-default-1",
          "Statement": [
            {
              "Sid": "Enable IAM User Permissions",
              "Effect": "Allow",
              "Principal": {
                "AWS": "arn:aws:iam::111122223333:root"
              },
              "Action": "kms:*",
              "Resource": "*"
            },
            {
              "Sid": "Allow administration of the key",
              "Effect": "Allow",
              "Principal": {
                "AWS": "arn:aws:iam::123456789012:user/Alice"
              },
              "Action": [
                "kms:Create*",
                "kms:Describe*",
                "kms:Enable*",
                "kms:List*",
                "kms:Put*",
                "kms:Update*",
                "kms:Revoke*",
                "kms:Disable*",
                "kms:Get*",
                "kms:Delete*",
                "kms:ScheduleKeyDeletion",
                "kms:CancelKeyDeletion"
              ],
              "Resource": "*"
            },
            {
              "Effect": "Allow",
              "Principal": {
                "AWS": "arn:aws:iam::123456789012:user/Bob"
              },
              "Action": [
                "kms:DescribeKey",
                "kms:Encrypt",
                "kms:Decrypt",
                "kms:ReEncrypt*",
                "kms:GenerateDataKey",
                "kms:GenerateDataKeyWithoutPlaintext"
              ],
              "Resource": "*",
              "Sid": "Allow use of the key"
            }
          ]
        }
      }
    }
  }
}