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Security group egress with all protocols

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Metadata

Id: cloudformation-aws-security-group-egress-with-all-protocols

Provider: AWS

Platform: CloudFormation

Severity: Medium

Category: Networking and Firewall

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Description

Egress rules that allow all protocols (IpProtocol: -1) permit unrestricted outbound traffic. This increases the risk of data exfiltration and enables command-and-control traffic or lateral movement.

For AWS::EC2::SecurityGroupEgress resources and entries in AWS::EC2::SecurityGroup > Properties.SecurityGroupEgress, IpProtocol must not be set to -1. Specify explicit protocols such as tcp, udp, or icmp. Resources with IpProtocol: -1 will be flagged. Instead, define explicit IpProtocol values and corresponding FromPort/ToPort for TCP/UDP, and restrict destination CIDRs or target security groups to the minimum required.

Secure configuration examples:

MySecurityGroup:
  Type: AWS::EC2::SecurityGroup
  Properties:
    GroupDescription: Allow outbound HTTPS only
    SecurityGroupEgress:
      - IpProtocol: tcp
        FromPort: 443
        ToPort: 443
        CidrIp: 0.0.0.0/0

MyEgressRule:
  Type: AWS::EC2::SecurityGroupEgress
  Properties:
    GroupId: !Ref MySecurityGroup
    IpProtocol: tcp
    FromPort: 443
    ToPort: 443
    CidrIp: 203.0.113.0/24

Compliant Code Examples

Resources:
  InstanceSecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Allow http to client host
      VpcId:
         Ref: myVPC
      SecurityGroupIngress:
      - IpProtocol: tcp
        FromPort: 80
        ToPort: 80
        CidrIp: 0.0.0.0/0
      SecurityGroupEgress:
      - IpProtocol: tcp
        FromPort: 80
        ToPort: 80
        CidrIp: 0.0.0.0/0
  OutboundRule:
    Type: AWS::EC2::SecurityGroupEgress
    Properties:
      IpProtocol: tcp
      FromPort: 0
      ToPort: 65535
      DestinationSecurityGroupId:
        Fn::GetAtt:
        - TargetSG
        - GroupId
      GroupId:
        Fn::GetAtt:
        - SourceSG
        - GroupId
  InboundRule:
    Type: AWS::EC2::SecurityGroupIngress
    Properties:
      IpProtocol: tcp
      FromPort: 0
      ToPort: 65535
      SourceSecurityGroupId:
        Fn::GetAtt:
        - SourceSG
        - GroupId
      GroupId:
        Fn::GetAtt:
        - TargetSG
        - GroupId

{
  "Resources": {
    "InstanceSecurityGroup": {
      "Type": "AWS::EC2::SecurityGroup",
      "Properties": {
        "GroupDescription": "Allow http to client host",
        "VpcId": {
          "Ref": "myVPC"
        },
        "SecurityGroupIngress": [
          {
            "IpProtocol": "tcp",
            "FromPort": 80,
            "ToPort": 80,
            "CidrIp": "0.0.0.0/0"
          }
        ],
        "SecurityGroupEgress": [
          {
            "IpProtocol": "tcp",
            "FromPort": 80,
            "ToPort": 80,
            "CidrIp": "0.0.0.0/0"
          }
        ]
      }
    },
    "OutboundRule": {
      "Type": "AWS::EC2::SecurityGroupEgress",
      "Properties": {
        "IpProtocol": "tcp",
        "FromPort": 0,
        "ToPort": 65535,
        "DestinationSecurityGroupId": {
          "Fn::GetAtt": [
            "TargetSG",
            "GroupId"
          ]
        },
        "GroupId": {
          "Fn::GetAtt": [
            "SourceSG",
            "GroupId"
          ]
        }
      }
    },
    "InboundRule": {
      "Type": "AWS::EC2::SecurityGroupIngress",
      "Properties": {
        "SourceSecurityGroupId": {
          "Fn::GetAtt": [
            "SourceSG",
            "GroupId"
          ]
        },
        "GroupId": {
          "Fn::GetAtt": [
            "TargetSG",
            "GroupId"
          ]
        },
        "IpProtocol": "tcp",
        "FromPort": 0,
        "ToPort": 65535
      }
    }
  }
}

Non-Compliant Code Examples

Resources:
  InstanceSecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
      GroupDescription: Allow http to client host
      VpcId:
         Ref: myVPC
      SecurityGroupIngress:
      - IpProtocol: -1
        FromPort: 80
        ToPort: 80
        CidrIp: 0.0.0.0/0
      SecurityGroupEgress:
      - IpProtocol: -1
        FromPort: 80
        ToPort: 80
        CidrIp: 0.0.0.0/0
  OutboundRule:
    Type: AWS::EC2::SecurityGroupEgress
    Properties:
      IpProtocol: -1
      FromPort: 0
      ToPort: 65535
      DestinationSecurityGroupId:
        Fn::GetAtt:
        - TargetSG
        - GroupId
      GroupId:
        Fn::GetAtt:
        - SourceSG
        - GroupId
  InboundRule:
    Type: AWS::EC2::SecurityGroupIngress
    Properties:
      IpProtocol: -1
      FromPort: 0
      ToPort: 65535
      SourceSecurityGroupId:
        Fn::GetAtt:
        - SourceSG
        - GroupId
      GroupId:
        Fn::GetAtt:
        - TargetSG
        - GroupId

{
  "Resources": {
    "InstanceSecurityGroup": {
      "Type": "AWS::EC2::SecurityGroup",
      "Properties": {
        "GroupDescription": "Allow http to client host",
        "VpcId": {
          "Ref": "myVPC"
        },
        "SecurityGroupIngress": [
          {
            "CidrIp": "0.0.0.0/0",
            "IpProtocol": -1,
            "FromPort": 80,
            "ToPort": 80
          }
        ],
        "SecurityGroupEgress": [
          {
            "CidrIp": "0.0.0.0/0",
            "IpProtocol": -1,
            "FromPort": 80,
            "ToPort": 80
          }
        ]
      }
    },
    "OutboundRule": {
      "Type": "AWS::EC2::SecurityGroupEgress",
      "Properties": {
        "DestinationSecurityGroupId": {
          "Fn::GetAtt": [
            "TargetSG",
            "GroupId"
          ]
        },
        "GroupId": {
          "Fn::GetAtt": [
            "SourceSG",
            "GroupId"
          ]
        },
        "IpProtocol": -1,
        "FromPort": 0,
        "ToPort": 65535
      }
    },
    "InboundRule": {
      "Properties": {
        "GroupId": {
          "Fn::GetAtt": [
            "TargetSG",
            "GroupId"
          ]
        },
        "IpProtocol": -1,
        "FromPort": 0,
        "ToPort": 65535,
        "SourceSecurityGroupId": {
          "Fn::GetAtt": [
            "SourceSG",
            "GroupId"
          ]
        }
      },
      "Type": "AWS::EC2::SecurityGroupIngress"
    }
  }
}