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Security group with unrestricted access to SSH

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Metadata

Id: cloudformation-aws-security-groups-with-unrestricted-access-to-ssh

Provider: AWS

Platform: CloudFormation

Severity: Medium

Category: Networking and Firewall

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Description

Allowing SSH (TCP port 22) from the public internet (0.0.0.0/0) exposes instances to brute-force attacks, credential theft, lateral movement, and unauthorized access. In CloudFormation AWS::EC2::SecurityGroup resources, any Properties.SecurityGroupIngress entry with CidrIp: 0.0.0.0/0 and FromPort or ToPort equal to 22 will be flagged.

To remediate, restrict SSH ingress to specific trusted IP ranges, use a bastion/jump host, or adopt AWS Systems Manager Session Manager instead of opening port 22. Resources containing the insecure ingress entry will be reported.

Secure configuration example (restrict SSH to a single IP):

MySecurityGroup:
  Type: AWS::EC2::SecurityGroup
  Properties:
    GroupDescription: Allow SSH from admin IP only
    SecurityGroupIngress:
      - IpProtocol: tcp
        FromPort: 22
        ToPort: 22
        CidrIp: 203.0.113.4/32

Note: this rule specifically matches ingress entries where FromPort == 22 or ToPort == 22; port ranges that include 22 but do not have 22 as an endpoint may not be detected by this check.

Compliant Code Examples

Resources:
  Ec2Instance:
    Type: 'AWS::EC2::Instance'
    Properties:
      SecurityGroups:
        - !Ref InstanceSecurityGroup
      KeyName: mykey
      ImageId: ''
  InstanceSecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
        GroupDescription: Allow http to client host
        VpcId:
          Ref: myVPC
        SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: 80
          ToPort: 80
          CidrIp: 127.0.0.1/32
        SecurityGroupEgress:
        - IpProtocol: tcp
          FromPort: 80
          ToPort: 80
          CidrIp: 127.0.0.1/33

{
  "Resources": {
    "InstanceSecurityGroup": {
      "Type": "AWS::EC2::SecurityGroup",
      "Properties": {
        "GroupDescription": "Allow http to client host",
        "VpcId": {
          "Ref": "myVPC"
        },
        "SecurityGroupIngress": [
          {
            "FromPort": 80,
            "ToPort": 80,
            "CidrIp": "127.0.0.1/32",
            "IpProtocol": "tcp"
          }
        ],
        "SecurityGroupEgress": [
          {
            "IpProtocol": "tcp",
            "FromPort": 80,
            "ToPort": 80,
            "CidrIp": "127.0.0.1/33"
          }
        ]
      }
    },
    "Ec2Instance": {
      "Type": "AWS::EC2::Instance",
      "Properties": {
        "SecurityGroups": [
          "InstanceSecurityGroup"
        ],
        "KeyName": "mykey",
        "ImageId": ""
      }
    }
  }
}

Non-Compliant Code Examples

Resources:
  Ec2Instance:
    Type: 'AWS::EC2::Instance'
    Properties:
      SecurityGroups:
        - !Ref InstanceSecurityGroup
      KeyName: mykey
      ImageId: ''
  InstanceSecurityGroup:
    Type: AWS::EC2::SecurityGroup
    Properties:
        GroupDescription: Allow http to client host
        VpcId:
          Ref: myVPC
        SecurityGroupIngress:
        - IpProtocol: tcp
          FromPort: 22
          ToPort: 22
          CidrIp: 0.0.0.0/0
        SecurityGroupEgress:
        - IpProtocol: tcp
          FromPort: 80
          ToPort: 80
          CidrIp: 0.0.0.0/0

{
  "Resources": {
    "Ec2Instance": {
      "Type": "AWS::EC2::Instance",
      "Properties": {
        "ImageId": "",
        "SecurityGroups": [
          "InstanceSecurityGroup"
        ],
        "KeyName": "mykey"
      }
    },
    "InstanceSecurityGroup": {
      "Properties": {
        "SecurityGroupEgress": [
          {
            "IpProtocol": "tcp",
            "FromPort": 80,
            "ToPort": 80,
            "CidrIp": "0.0.0.0/0"
          }
        ],
        "GroupDescription": "Allow http to client host",
        "VpcId": {
          "Ref": "myVPC"
        },
        "SecurityGroupIngress": [
          {
            "ToPort": 22,
            "CidrIp": "0.0.0.0/0",
            "IpProtocol": "tcp",
            "FromPort": 22
          }
        ]
      },
      "Type": "AWS::EC2::SecurityGroup"
    }
  }
}