Security Group Ingress Has CIDR Not Recommended

• Query id: a3e4e39a-e5fc-4ee9-8cf5-700febfa86dd
• Query name: Security Group Ingress Has CIDR Not Recommended
• Platform: CloudFormation
• Severity: Low
• Category: Best Practices
• URL: Github

Description

AWS Security Group Ingress CIDR should not be /32 in case of IPV4 or /128 in case of IPV6
Documentation

Code samples

Code samples with security vulnerabilities

Postitive test num. 1 - yaml file

Resources:
  InstanceSecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Allow http to client host
      VpcId:
         Ref: myVPC
      SecurityGroupIngress:
      - IpProtocol: tcp
        Description: TCP
        FromPort: 80
        ToPort: 80
        CidrIp: 122.24.0.0/32
      SecurityGroupEgress:
      - IpProtocol: tcp
        Description: TCP
        FromPort: 80
        ToPort: 80
        CidrIp: 192.0.2.0/24
  OutboundRule:
    Type: AWS::EC2::SecurityGroupEgress
    Properties:
      Description: TCP
      IpProtocol: tcp
      FromPort: 0
      ToPort: 65535
      CidrIp: 192.0.2.0/24
      DestinationSecurityGroupId:
        Fn::GetAtt:
        - TargetSG
        - GroupId
      GroupId:
        Fn::GetAtt:
        - SourceSG
        - GroupId
  InboundRule:
    Type: AWS::EC2::SecurityGroupIngress
    Properties:
      Description: TCP
      IpProtocol: tcp
      FromPort: 0
      ToPort: 65535
      CidrIpv6: ::/128
      SourceSecurityGroupId:
        Fn::GetAtt:
        - SourceSG
        - GroupId
      GroupId:
        Fn::GetAtt:
        - TargetSG
        - GroupId

Postitive test num. 2 - json file

{
  "Resources": {
    "OutboundRule": {
      "Type": "AWS::EC2::SecurityGroupEgress",
      "Properties": {
        "ToPort": 65535,
        "CidrIp": "192.0.2.0/24",
        "DestinationSecurityGroupId": {
          "Fn::GetAtt": [
            "TargetSG",
            "GroupId"
          ]
        },
        "GroupId": {
          "Fn::GetAtt": [
            "SourceSG",
            "GroupId"
          ]
        },
        "Description": "TCP",
        "IpProtocol": "tcp",
        "FromPort": 0
      }
    },
    "InboundRule": {
      "Type": "AWS::EC2::SecurityGroupIngress",
      "Properties": {
        "SourceSecurityGroupId": {
          "Fn::GetAtt": [
            "SourceSG",
            "GroupId"
          ]
        },
        "GroupId": {
          "Fn::GetAtt": [
            "TargetSG",
            "GroupId"
          ]
        },
        "Description": "TCP",
        "IpProtocol": "tcp",
        "FromPort": 0,
        "ToPort": 65535,
        "CidrIpv6": "::/128"
      }
    },
    "InstanceSecurityGroup": {
      "Type": "AWS::EC2::SecurityGroup",
      "Properties": {
        "SecurityGroupEgress": [
          {
            "ToPort": 80,
            "CidrIp": "192.0.2.0/24",
            "IpProtocol": "tcp",
            "Description": "TCP",
            "FromPort": 80
          }
        ],
        "GroupDescription": "Allow http to client host",
        "VpcId": {
          "Ref": "myVPC"
        },
        "SecurityGroupIngress": [
          {
            "IpProtocol": "tcp",
            "Description": "TCP",
            "FromPort": 80,
            "ToPort": 80,
            "CidrIp": "122.24.0.0/32"
          }
        ]
      }
    }
  }
}

Code samples without security vulnerabilities

Negative test num. 1 - yaml file

Resources:
  InstanceSecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Allow http to client host
      VpcId:
         Ref: myVPC
      SecurityGroupIngress:
      - IpProtocol: tcp
        Description: TCP
        FromPort: 80
        ToPort: 80
        CidrIp: 192.0.2.0/24
      SecurityGroupEgress:
      - IpProtocol: tcp
        Description: TCP
        FromPort: 80
        ToPort: 80
        CidrIp: 192.0.2.0/24
  OutboundRule:
    Type: AWS::EC2::SecurityGroupEgress
    Properties:
      Description: TCP
      IpProtocol: tcp
      FromPort: 0
      ToPort: 0
      CidrIp: 192.0.2.0/24
      DestinationSecurityGroupId:
        Fn::GetAtt:
        - TargetSG
        - GroupId
      GroupId:
        Fn::GetAtt:
        - SourceSG
        - GroupId
  InboundRule:
    Type: AWS::EC2::SecurityGroupIngress
    Properties:
      Description: TCP
      IpProtocol: tcp
      FromPort: 0
      ToPort: 0
      CidrIpv6: 2001:0DB8:1234::/48
      SourceSecurityGroupId:
        Fn::GetAtt:
        - SourceSG
        - GroupId
      GroupId:
        Fn::GetAtt:
        - TargetSG
        - GroupId

Negative test num. 2 - json file

{
  "Resources": {
    "InstanceSecurityGroup": {
      "Properties": {
        "VpcId": {
          "Ref": "myVPC"
        },
        "SecurityGroupIngress": [
          {
            "IpProtocol": "tcp",
            "Description": "TCP",
            "FromPort": 80,
            "ToPort": 80,
            "CidrIp": "192.0.2.0/24"
          }
        ],
        "SecurityGroupEgress": [
          {
            "ToPort": 80,
            "CidrIp": "192.0.2.0/24",
            "IpProtocol": "tcp",
            "Description": "TCP",
            "FromPort": 80
          }
        ],
        "GroupDescription": "Allow http to client host"
      },
      "Type": "AWS::EC2::SecurityGroup"
    },
    "OutboundRule": {
      "Type": "AWS::EC2::SecurityGroupEgress",
      "Properties": {
        "ToPort": 0,
        "CidrIp": "192.0.2.0/24",
        "DestinationSecurityGroupId": {
          "Fn::GetAtt": [
            "TargetSG",
            "GroupId"
          ]
        },
        "GroupId": {
          "Fn::GetAtt": [
            "SourceSG",
            "GroupId"
          ]
        },
        "Description": "TCP",
        "IpProtocol": "tcp",
        "FromPort": 0
      }
    },
    "InboundRule": {
      "Type": "AWS::EC2::SecurityGroupIngress",
      "Properties": {
        "ToPort": 0,
        "CidrIpv6": "2001:0DB8:1234::/48",
        "SourceSecurityGroupId": {
          "Fn::GetAtt": [
            "SourceSG",
            "GroupId"
          ]
        },
        "GroupId": {
          "Fn::GetAtt": [
            "TargetSG",
            "GroupId"
          ]
        },
        "Description": "TCP",
        "IpProtocol": "tcp",
        "FromPort": 0
      }
    }
  }
}