For AI agents: A markdown version of this page is available at https://docs.datadoghq.com/security/code_security/iac_security/iac_rules/cloudformation-aws-security-group-ingress-has-cidr-not-recommended.md. A documentation index is available at /llms.txt.

Security group ingress has CIDR not recommended

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Metadata

Id: cloudformation-aws-security-group-ingress-has-cidr-not-recommended

Provider: AWS

Platform: CloudFormation

Severity: Low

Category: Best Practices

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Description

Ingress rules that use single-address CIDRs (IPv4 /32 or IPv6 /128) are brittle. They often indicate hard-coded, single-IP access which can become stale, break when addresses are reassigned, and lead to unintended access or operational disruption.

This check inspects AWS::EC2::SecurityGroupIngress resources (Properties.CidrIp and Properties.CidrIpv6) and AWS::EC2::SecurityGroup resources’ Properties.SecurityGroupIngress[].CidrIp and CidrIpv6 entries. Any entry containing /32 (IPv4) or /128 (IPv6) will be flagged.

To remediate, avoid hard-coding single IPs by using SourceSecurityGroupId, AWS managed prefix lists, or appropriately scoped network CIDRs that reflect your trusted network. If a single-IP exception is required, document the justification and maintain a process to review and update it.

Secure configuration example (use security group reference instead of single IP):

MySecurityGroup:
  Type: AWS::EC2::SecurityGroup
  Properties:
    GroupDescription: Web server security group
    VpcId: !Ref MyVPC
    SecurityGroupIngress:
      - IpProtocol: tcp
        FromPort: 443
        ToPort: 443
        SourceSecurityGroupId: !Ref BastionSecurityGroup

Compliant Code Examples

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

{
  "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
      }
    }
  }
}

Non-Compliant Code Examples

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

{
  "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"
          }
        ]
      }
    }
  }
}