Lambda Permission Principal Is Wildcard

• Query id: 1d6e16f1-5d8a-4379-bfb3-2dadd38ed5a7
• Query name: Lambda Permission Principal Is Wildcard
• Platform: CloudFormation
• Severity: Medium
• Category: Access Control
• URL: Github

Description

Lambda Permission Principal should not contain a wildcard.
Documentation

Code samples

Code samples with security vulnerabilities

Positive test num. 1 - yaml file

AWSTemplateFormatVersion: "2010-09-09"
Description: Creates RDS Cluster
Resources:
  s3Permission:
    Type: AWS::Lambda::Permission
    Properties:
      FunctionName: !GetAtt function.Arn
      Action: lambda:InvokeFunction
      Principal: '*'
      SourceAccount: !Ref 'AWS::AccountId'
      SourceArn: !GetAtt bucket.Arn

Positive test num. 2 - json file

{
  "Resources": {
    "s3Permission": {
      "Type": "AWS::Lambda::Permission",
      "Properties": {
        "SourceAccount": "AWS::AccountId",
        "SourceArn": "bucket.Arn",
        "FunctionName": "function.Arn",
        "Action": "lambda:InvokeFunction",
        "Principal": "*"
      }
    }
  },
  "AWSTemplateFormatVersion": "2010-09-09",
  "Description": "Creates RDS Cluster"
}

Code samples without security vulnerabilities

Negative test num. 1 - yaml file

AWSTemplateFormatVersion: "2010-09-09"
Description: Creates RDS Cluster
Resources:
  s3Permission:
    Type: AWS::Lambda::Permission
    Properties:
      FunctionName: !GetAtt function.Arn
      Action: lambda:InvokeFunction
      Principal: s3.amazonaws.com
      SourceAccount: !Ref 'AWS::AccountId'
      SourceArn: !GetAtt bucket.Arn

Negative test num. 2 - json file

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Description": "Creates RDS Cluster",
  "Resources": {
    "s3Permission": {
      "Type": "AWS::Lambda::Permission",
      "Properties": {
        "FunctionName": "function.Arn",
        "Action": "lambda:InvokeFunction",
        "Principal": "s3.amazonaws.com",
        "SourceAccount": "AWS::AccountId",
        "SourceArn": "bucket.Arn"
      }
    }
  }
}