EC2 Network ACL Overlapping Ports

• Query id: 77b6f1e2-bde4-4a6a-ae7e-a40659ff1576
• Query name: EC2 Network ACL Overlapping Ports
• Platform: CloudFormation
• Severity: Medium
• Category: Networking and Firewall
• URL: Github

Description

NetworkACL Entries are reusing or overlapping ports which may create ineffective rules
Documentation

Code samples

Code samples with security vulnerabilities

Positive test num. 1 - yaml file

Resources:
  MyNACL:
    Type: AWS::EC2::NetworkAcl
    Properties:
       VpcId: vpc-1122334455aabbccd
       Tags:
       - Key: Name
         Value: NACLforSSHTraffic
  InboundRule:
    Type: AWS::EC2::NetworkAclEntry
    Properties:
       NetworkAclId:
         Ref: MyNACL
       RuleNumber: 100
       Protocol: 6
       RuleAction: allow
       CidrBlock: 172.16.0.0/24
       PortRange:
         From: 13
         To: 22
  OutboundRule:
    Type: AWS::EC2::NetworkAclEntry
    Properties:
       NetworkAclId:
         Ref: MyNACL
       RuleNumber: 100
       Protocol: 6
       RuleAction: allow
       CidrBlock: 173.20.0.0/24
       PortRange:
         From: 12
         To: 20
  OutboundTests:
    Type: AWS::EC2::NetworkAclEntry
    Properties:
       NetworkAclId:
         Ref: MyNACL
       RuleNumber: 100
       Protocol: 6
       RuleAction: allow
       CidrBlock: 175.20.0.0/24
       PortRange:
         From: 20
         To: 25
  InboundTests:
    Type: AWS::EC2::NetworkAclEntry
    Properties:
       NetworkAclId:
         Ref: MyNACL
       RuleNumber: 100
       Protocol: 6
       RuleAction: allow
       CidrBlock: 151.20.0.0/24
       PortRange:
         From: 6
         To: 13
  Default:
    Type: AWS::EC2::NetworkAclEntry
    Properties:
       NetworkAclId:
         Ref: MyNACL
       RuleNumber: 100
       Protocol: 6
       RuleAction: allow
       CidrBlock: 150.20.0.0/24
       PortRange:
         From: 1
         To: 2
  Match:
    Type: AWS::EC2::NetworkAclEntry
    Properties:
       NetworkAclId:
         Ref: MyNACL
       RuleNumber: 100
       Protocol: 6
       RuleAction: allow
       CidrBlock: 121.20.0.0/24
       PortRange:
         From: 3
         To: 5
  EqualMatch:
    Type: AWS::EC2::NetworkAclEntry
    Properties:
       NetworkAclId:
         Ref: MyNACL
       RuleNumber: 100
       Protocol: 6
       RuleAction: allow
       CidrBlock: 120.20.0.0/24
       PortRange:
         From: 3
         To: 5

Positive test num. 2 - json file

{
  "Resources": {
    "Default": {
      "Type": "AWS::EC2::NetworkAclEntry",
      "Properties": {
        "NetworkAclId": {
          "Ref": "MyNACL"
        },
        "RuleNumber": 100,
        "Protocol": 6,
        "RuleAction": "allow",
        "CidrBlock": "150.20.0.0/24",
        "PortRange": {
          "From": 1,
          "To": 2
        }
      }
    },
    "Match": {
      "Type": "AWS::EC2::NetworkAclEntry",
      "Properties": {
        "PortRange": {
          "From": 3,
          "To": 5
        },
        "NetworkAclId": {
          "Ref": "MyNACL"
        },
        "RuleNumber": 100,
        "Protocol": 6,
        "RuleAction": "allow",
        "CidrBlock": "121.20.0.0/24"
      }
    },
    "EqualMatch": {
      "Properties": {
        "CidrBlock": "120.20.0.0/24",
        "PortRange": {
          "From": 3,
          "To": 5
        },
        "NetworkAclId": {
          "Ref": "MyNACL"
        },
        "RuleNumber": 100,
        "Protocol": 6,
        "RuleAction": "allow"
      },
      "Type": "AWS::EC2::NetworkAclEntry"
    },
    "MyNACL": {
      "Type": "AWS::EC2::NetworkAcl",
      "Properties": {
        "VpcId": "vpc-1122334455aabbccd",
        "Tags": [
          {
            "Key": "Name",
            "Value": "NACLforSSHTraffic"
          }
        ]
      }
    },
    "InboundRule": {
      "Type": "AWS::EC2::NetworkAclEntry",
      "Properties": {
        "NetworkAclId": {
          "Ref": "MyNACL"
        },
        "RuleNumber": 100,
        "Protocol": 6,
        "RuleAction": "allow",
        "CidrBlock": "172.16.0.0/24",
        "PortRange": {
          "From": 13,
          "To": 22
        }
      }
    },
    "OutboundRule": {
      "Type": "AWS::EC2::NetworkAclEntry",
      "Properties": {
        "PortRange": {
          "From": 12,
          "To": 20
        },
        "NetworkAclId": {
          "Ref": "MyNACL"
        },
        "RuleNumber": 100,
        "Protocol": 6,
        "RuleAction": "allow",
        "CidrBlock": "173.20.0.0/24"
      }
    },
    "OutboundTests": {
      "Type": "AWS::EC2::NetworkAclEntry",
      "Properties": {
        "NetworkAclId": {
          "Ref": "MyNACL"
        },
        "RuleNumber": 100,
        "Protocol": 6,
        "RuleAction": "allow",
        "CidrBlock": "175.20.0.0/24",
        "PortRange": {
          "From": 20,
          "To": 25
        }
      }
    },
    "InboundTests": {
      "Type": "AWS::EC2::NetworkAclEntry",
      "Properties": {
        "RuleAction": "allow",
        "CidrBlock": "151.20.0.0/24",
        "PortRange": {
          "From": 6,
          "To": 13
        },
        "NetworkAclId": {
          "Ref": "MyNACL"
        },
        "RuleNumber": 100,
        "Protocol": 6
      }
    }
  }
}

Code samples without security vulnerabilities

Negative test num. 1 - yaml file

Resources:
  MyNACL:
    Type: AWS::EC2::NetworkAcl
    Properties:
       VpcId: vpc-1122334455aabbccd
       Tags:
       - Key: Name
         Value: NACLforSSHTraffic
  InboundRule:
    Type: AWS::EC2::NetworkAclEntry
    Properties:
       NetworkAclId:
         Ref: MyNACL
       RuleNumber: 100
       Protocol: 6
       RuleAction: allow
       CidrBlock: 172.16.0.0/24
       PortRange:
         From: 13
         To: 22
  OutboundRule:
    Type: AWS::EC2::NetworkAclEntry
    Properties:
       NetworkAclId:
         Ref: MyNACL
       RuleNumber: 100
       Protocol: 6
       RuleAction: allow
       CidrBlock: 173.20.0.0/24
       PortRange:
         From: 24
         To: 25

Negative test num. 2 - json file

{
  "Resources": {
    "MyNACL": {
      "Type": "AWS::EC2::NetworkAcl",
      "Properties": {
        "VpcId": "vpc-1122334455aabbccd",
        "Tags": [
          {
            "Key": "Name",
            "Value": "NACLforSSHTraffic"
          }
        ]
      }
    },
    "InboundRule": {
      "Properties": {
        "NetworkAclId": {
          "Ref": "MyNACL"
        },
        "RuleNumber": 100,
        "Protocol": 6,
        "RuleAction": "allow",
        "CidrBlock": "172.16.0.0/24",
        "PortRange": {
          "From": 13,
          "To": 22
        }
      },
      "Type": "AWS::EC2::NetworkAclEntry"
    },
    "OutboundRule": {
      "Type": "AWS::EC2::NetworkAclEntry",
      "Properties": {
        "NetworkAclId": {
          "Ref": "MyNACL"
        },
        "RuleNumber": 100,
        "Protocol": 6,
        "RuleAction": "allow",
        "CidrBlock": "173.20.0.0/24",
        "PortRange": {
          "From": 24,
          "To": 25
        }
      }
    }
  }
}