EC2 Network ACL Ineffective Denied Traffic

• Query id: 2623d682-dccb-44cd-99d0-54d9fd62f8f2
• Query name: EC2 Network ACL Ineffective Denied Traffic
• Platform: CloudFormation
• Severity: Medium
• Category: Access Control
• URL: Github

Description

Ineffective deny rules. A deny rule should be applied to all IP addresses.
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: deny
       CidrBlock: 172.16.0.0/24
       PortRange:
         From: 22
         To: 22
  OutboundRule:
    Type: AWS::EC2::NetworkAclEntry
    Properties:
       NetworkAclId:
         Ref: MyNACL
       RuleNumber: 100
       Protocol: -1
       Egress: true
       RuleAction: deny
       CidrBlock: 0.0.0.0/0

Positive test num. 2 - json file

{
  "Resources": {
    "MyNACL": {
      "Type": "AWS::EC2::NetworkAcl",
      "Properties": {
        "VpcId": "vpc-1122334455aabbccd",
        "Tags": [
          {
            "Key": "Name",
            "Value": "NACLforSSHTraffic"
          }
        ]
      }
    },
    "InboundRule": {
      "Properties": {
        "RuleNumber": 100,
        "Protocol": 6,
        "RuleAction": "deny",
        "CidrBlock": "172.16.0.0/24",
        "PortRange": {
          "From": 22,
          "To": 22
        },
        "NetworkAclId": {
          "Ref": "MyNACL"
        }
      },
      "Type": "AWS::EC2::NetworkAclEntry"
    },
    "OutboundRule": {
      "Properties": {
        "RuleAction": "deny",
        "CidrBlock": "0.0.0.0/0",
        "NetworkAclId": {
          "Ref": "MyNACL"
        },
        "RuleNumber": 100,
        "Protocol": -1,
        "Egress": true
      },
      "Type": "AWS::EC2::NetworkAclEntry"
    }
  }
}

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: 22
         To: 22
  OutboundRule:
    Type: AWS::EC2::NetworkAclEntry
    Properties:
       NetworkAclId:
         Ref: MyNACL
       RuleNumber: 100
       Protocol: -1
       Egress: true
       RuleAction: allow
       CidrBlock: 0.0.0.0/0

Negative test num. 2 - json file

{
  "Resources": {
    "MyNACL": {
      "Properties": {
        "VpcId": "vpc-1122334455aabbccd",
        "Tags": [
          {
            "Key": "Name",
            "Value": "NACLforSSHTraffic"
          }
        ]
      },
      "Type": "AWS::EC2::NetworkAcl"
    },
    "InboundRule": {
      "Type": "AWS::EC2::NetworkAclEntry",
      "Properties": {
        "RuleAction": "allow",
        "CidrBlock": "172.16.0.0/24",
        "PortRange": {
          "From": 22,
          "To": 22
        },
        "NetworkAclId": {
          "Ref": "MyNACL"
        },
        "RuleNumber": 100,
        "Protocol": 6
      }
    },
    "OutboundRule": {
      "Type": "AWS::EC2::NetworkAclEntry",
      "Properties": {
        "NetworkAclId": {
          "Ref": "MyNACL"
        },
        "RuleNumber": 100,
        "Protocol": -1,
        "Egress": true,
        "RuleAction": "allow",
        "CidrBlock": "0.0.0.0/0"
      }
    }
  }
}