Public Lambda via API Gateway

• Query id: 57b12981-3816-4c31-b190-a1e614361dd2
• Query name: Public Lambda via API Gateway
• Platform: CloudFormation
• Severity: Medium
• Category: Access Control
• URL: Github

Description

Allowing to run lambda function using public API Gateway
Documentation

Code samples

Code samples with security vulnerabilities

Positive test num. 1 - yaml file

AWSTemplateFormatVersion: "2010-09-09"
Description: "BatchJobDefinition"
Resources:
  s3Permission3:
    Type: AWS::Lambda::Permission
    Properties:
      FunctionName: !GetAtt function.Arn
      Action: lambda:InvokeFunction
      Principal: apigateway.amazonaws.com
      SourceAccount: !Ref 'AWS::AccountId'
      SourceArn: arn:aws:s3:eu-central-1:123456789012/*/*

Positive test num. 2 - json file

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Resources": {
    "s3Permission": {
      "Type": "AWS::Lambda::Permission",
      "Properties": {
        "FunctionName": {
          "Fn::GetAtt": [
            "function",
            "Arn"
          ]
        },
        "Action": "lambda:InvokeFunction",
        "Principal": "apigateway.amazonaws.com",
        "SourceAccount": {
          "Ref": "AWS::AccountId"
        },
        "SourceArn": "arn:aws:s3:eu-central-1:123456789012/*/*"
      }
    }
  }
}

Code samples without security vulnerabilities

Negative test num. 1 - yaml file

AWSTemplateFormatVersion: "2010-09-09"
Description: "BatchJobDefinition"
Resources:
  s3Permission3:
    Type: AWS::Lambda::Permission
    Properties:
      FunctionName: !GetAtt function.Arn
      Action: lambda:InvokeFunction
      Principal: s3.amazonaws.com
      SourceAccount: !Ref 'AWS::AccountId'
      SourceArn: arn:aws:s3:eu-central-1:123456789012:bucketname

Negative test num. 2 - json file

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Resources": {
    "s3Permission": {
      "Type": "AWS::Lambda::Permission",
      "Properties": {
        "FunctionName": {
          "Fn::GetAtt": [
            "function",
            "Arn"
          ]
        },
        "Action": "lambda:InvokeFunction",
        "Principal": "s3.amazonaws.com",
        "SourceAccount": {
          "Ref": "AWS::AccountId"
        },
        "SourceArn": "arn:aws:s3:eu-central-1:123456789012:bucketname"
      }
    }
  }
}