IAM Policy Grants 'AssumeRole' Permission Across All Services

• Query id: e835bd0d-65da-49f7-b6d1-b646da8727e6
• Query name: IAM Policy Grants 'AssumeRole' Permission Across All Services
• Platform: CloudFormation
• Severity: Medium
• Category: Access Control
• URL: Github

Description

IAM Policy should not grant 'AssumeRole' permission across all services.
Documentation

Code samples

Code samples with security vulnerabilities

Positive test num. 1 - yaml file

AWSTemplateFormatVersion: "2010-09-09"
Description: A sample template
Resources:
  mypolicy:
    Type: AWS::IAM::Policy
    Properties:
      PolicyName: mygrouppolicy
      PolicyDocument:
        Version: '2012-10-17'
        Statement:
        - Effect: Allow
          Action: ["sts:AssumeRole"]
          Resource: "*"
      Users: ["SomeUser"]

Positive test num. 2 - json file

{
  "Description": "A sample template",
  "Resources": {
    "mypolicy": {
      "Type": "AWS::IAM::Policy",
      "Properties": {
        "PolicyName": "mygrouppolicy",
        "PolicyDocument": {
          "Version": "2012-10-17",
          "Statement": [
            {
              "Effect": "Allow",
              "Action": [
                "sts:AssumeRole"
              ],
              "Resource": "*"
            }
          ]
        },
        "Users": [
          "SomeUser"
        ]
      }
    }
  },
  "AWSTemplateFormatVersion": "2010-09-09"
}

Code samples without security vulnerabilities

Negative test num. 1 - yaml file

AWSTemplateFormatVersion: "2010-09-09"
Description: A sample template
Resources:
  MyPolicy:
    Type: AWS::IAM::Policy
    Properties:
      PolicyName: mygrouppolicy
      PolicyDocument:
        Version: "2012-10-17"
        Statement:
          - Effect: Allow
            Action:
              - s3:GetObject
              - s3:PutObject
              - s3:PutObjectAcl
            Resource: arn:aws:s3:::myAWSBucket/*
      Groups:
        - myexistinggroup1
        - !Ref mygroup

Negative test num. 2 - json file

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Description": "A sample template",
  "Resources": {
    "MyPolicy": {
      "Type": "AWS::IAM::Policy",
      "Properties": {
        "PolicyName": "mygrouppolicy",
        "PolicyDocument": {
          "Version": "2012-10-17",
          "Statement": [
            {
              "Effect": "Allow",
              "Action": [
                "s3:GetObject",
                "s3:PutObject",
                "s3:PutObjectAcl"
              ],
              "Resource": "arn:aws:s3:::myAWSBucket/*"
            }
          ]
        },
        "Groups": [
          "myexistinggroup1",
          "mygroup"
        ]
      }
    }
  }
}