# ###################################
##       Rule Specification        ##
#####################################
# 
# Rule Identifier:
#   vpc_sg_restricted_common_ports_check
# 
# Description:
#   This control checks whether an Amazon EC2 security group rule that contains the strings '0.0.0.0/0' or '::/0' as a source IP range does not allow incoming TCP, UDP, ICMP, ICMPv6 traffic to the following ports: '3389', '20', '23', '110', '143', '3306', '8080', '1433', '9200', '9300', '25', '445', '135', '21', '1434', '4333', '5432', '5500', '5601', '22', '3000', '5000', '8088', '8888'.
# 
# Reports on:
#   AWS::EC2::SecurityGroup, AWS::EC2::SecurityGroupIngress
# 
# Evaluates:
#   AWS CloudFormation, AWS CloudFormation Hook
# 
# Rule Parameters:
#   None
# 
# Scenarios:
#   Scenario: 1
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document does not contain any EC2 security group or EC2 security group ingress resources
#      Then: SKIP
#   Scenario: 2
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an EC2 security group resource or EC2 security group ingress resource
#       And: The EC2 security group or EC2 security group ingress resource does not allow inbound traffic from a source
#            prefix list and has no rules allowing inbound traffic from '0.0.0.0/0' or '::/0' 
#      Then: SKIP
#   Scenario: 3
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an EC2 security group resource or EC2 security group ingress resource
#       And: The EC2 security group or EC2 security group ingress resource has rules allowing inbound traffic
#            from a source prefix list, '0.0.0.0/0' or '::/0'
#       And: EC2 security group or EC2 security group ingress resource has a rule that allows all traffic
#            ('IpProtocol' is set to '-1' or another protocol number)
#      Then: FAIL
#   Scenario: 4
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an EC2 security group resource or EC2 security group ingress resource
#       And: The EC2 security group or EC2 security group ingress resource has rules allowing inbound traffic
#            from a source prefix list, '0.0.0.0/0' or '::/0'
#       And: EC2 security group or EC2 security group ingress resource has no rules that allow all traffic
#            ('IpProtocol' is not set to '-1' or another protocol number)
#       And: Ports allowed are in the list of blocked ports
#      Then: FAIL
#   Scenario: 5
#     Given: The input document is an AWS CloudFormation or CloudFormation hook document
#       And: The input document contains an EC2 security group resource or EC2 security group ingress resource
#       And: The EC2 security group or EC2 security group ingress resource has rules allowing inbound traffic
#            from a source prefix list, '0.0.0.0/0' or '::/0'
#       And: EC2 security group or EC2 security group ingress resource has no rules that allow all traffic
#            ('IpProtocol' is not set to '-1' or another protocol number)
#       And: Ports allowed are not in the list of blocked ports
#      Then: PASS

#
# Constants
#
let SECURITY_GROUP_TYPE = "AWS::EC2::SecurityGroup"
let SECURITY_GROUP_INGRESS_TYPE = "AWS::EC2::SecurityGroupIngress"
let BLOCKED_PORTS = [3389, 20, 23, 110, 143, 3306, 8080, 1433, 9200, 9300, 25, 445, 135, 21, 1434, 4333, 5432, 5500,
                     5601, 22, 3000, 5000, 8088, 8888]
let AUTHORIZED_PROTOCOLS = ["tcp", "udp", "icmp", "icmpv6"]
let UNRESTRICTED_IPV4_RANGES = ["0.0.0.0/0"]
let UNRESTRICTED_IPV6_RANGES = ["::/0"]
let INPUT_DOCUMENT = this

#
# Assignments
#
let ec2_security_groups = Resources[
    Type == %SECURITY_GROUP_TYPE
]
let ec2_security_group_ingress_rules = Resources[
    Type == %SECURITY_GROUP_INGRESS_TYPE
]

#
# Primary Rules
#
rule vpc_sg_restricted_common_ports_check when is_cfn_template(%INPUT_DOCUMENT)
                                               %ec2_security_groups not empty {

    check_security_group(%ec2_security_groups.Properties)
        <<
        [CT.EC2.PR.4]: Require that any Amazon EC2 security group rule does not use the source IP range 0.0.0.0/0 or ::/0 for specific high-risk ports
        [FIX]: Remove Amazon EC2 security group ingress rules that allow traffic from '0.0.0.0/0' or '::/0' to high risk ports: '3389', '20', '23', '110', '143', '3306', '8080', '1433', '9200', '9300', '25', '445', '135', '21', '1434', '4333', '5432', '5500', '5601', '22', '3000', '5000', '8088', '8888'. The use of managed prefix lists is not supported.
        >>
}

rule vpc_sg_restricted_common_ports_check when is_cfn_template(%INPUT_DOCUMENT)
                                               %ec2_security_group_ingress_rules not empty {

    check_ingress_rule(%ec2_security_group_ingress_rules.Properties)
        <<
        [CT.EC2.PR.4]: Require that any Amazon EC2 security group rule does not use the source IP range 0.0.0.0/0 or ::/0 for specific high-risk ports
        [FIX]: Remove Amazon EC2 security group ingress rules that allow traffic from '0.0.0.0/0' or '::/0' to high risk ports: '3389', '20', '23', '110', '143', '3306', '8080', '1433', '9200', '9300', '25', '445', '135', '21', '1434', '4333', '5432', '5500', '5601', '22', '3000', '5000', '8088', '8888'. The use of managed prefix lists is not supported.
        >>
}

rule vpc_sg_restricted_common_ports_check when is_cfn_hook(%INPUT_DOCUMENT, %SECURITY_GROUP_TYPE) {

    check_security_group(%INPUT_DOCUMENT.%SECURITY_GROUP_TYPE.resourceProperties)
        <<
        [CT.EC2.PR.4]: Require that any Amazon EC2 security group rule does not use the source IP range 0.0.0.0/0 or ::/0 for specific high-risk ports
        [FIX]: Remove Amazon EC2 security group ingress rules that allow traffic from '0.0.0.0/0' or '::/0' to high risk ports: '3389', '20', '23', '110', '143', '3306', '8080', '1433', '9200', '9300', '25', '445', '135', '21', '1434', '4333', '5432', '5500', '5601', '22', '3000', '5000', '8088', '8888'. The use of managed prefix lists is not supported.
        >>
}

rule vpc_sg_restricted_common_ports_check when is_cfn_hook(%INPUT_DOCUMENT, %SECURITY_GROUP_INGRESS_TYPE) {

    check_ingress_rule(%INPUT_DOCUMENT.%SECURITY_GROUP_INGRESS_TYPE.resourceProperties)
        <<
        [CT.EC2.PR.4]: Require that any Amazon EC2 security group rule does not use the source IP range 0.0.0.0/0 or ::/0 for specific high-risk ports
        [FIX]: Remove Amazon EC2 security group ingress rules that allow traffic from '0.0.0.0/0' or '::/0' to high risk ports: '3389', '20', '23', '110', '143', '3306', '8080', '1433', '9200', '9300', '25', '445', '135', '21', '1434', '4333', '5432', '5500', '5601', '22', '3000', '5000', '8088', '8888'. The use of managed prefix lists is not supported.
        >>
}

#
# Parameterized Rules
#
rule check_security_group(security_group) {
    %security_group [
        SecurityGroupIngress exists
        SecurityGroupIngress is_list
        SecurityGroupIngress not empty
    ] {
        SecurityGroupIngress[*] {
            check_ingress_rule(this)
        }
    }
}

rule check_ingress_rule(ingress_rule) {
    %ingress_rule[ CidrIp in %UNRESTRICTED_IPV4_RANGES or
                   CidrIpv6 in %UNRESTRICTED_IPV6_RANGES or 
                   SourcePrefixListId exists ] {
        # Scenario 3
        IpProtocol exists
        IpProtocol in %AUTHORIZED_PROTOCOLS

        when IpProtocol in ["tcp", "udp"] {
            FromPort exists
            ToPort exists

            let ingress_block = this

            %BLOCKED_PORTS.* {
                # Scenarios 4 and 5
                check_ports(this, %ingress_block.FromPort, %ingress_block.ToPort)
            }
        }
    }
}

rule check_ports(port, FromPort, ToPort) {
    %FromPort > %port or
    %ToPort < %port
}

#
# Utility Rules
#
rule is_cfn_template(doc) {
    %doc {
        AWSTemplateFormatVersion exists  or
        Resources exists
    }
}

rule is_cfn_hook(doc, RESOURCE_TYPE) {
    %doc.%RESOURCE_TYPE.resourceProperties exists
}