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Unrestricted Security Group Ingress on Uncommon Ports

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Risk Level: High (act today)
Rule ID: EC2-034

Ensure that your Amazon EC2 security groups don't allow unrestricted access (i.e. 0.0.0.0/0 or ::/0) on uncommon ports in order to protect against attackers that use brute force methods to gain access to the EC2 instances associated with your security groups. An uncommon port can be any TCP/UDP port that is not included in the common service ports category, i.e. other than the commonly used ports such as 80 (HTTP), 443 (HTTPS), 20/21 (FTP), 22 (SSH), 23 (Telnet), 53 (DNS), 3389 (RDP), 25/465/587 (SMTP), 3306 (MySQL), 5432 (PostgreSQL), 1521 (Oracle Database), 1433 (SQL Server), 135 (RPC), and 137/138/139/445 (SMB/CIFS).

This rule can help you with the following compliance standards:

  • PCI
  • HIPAA
  • APRA
  • MAS
  • NIST4

For further details on compliance standards supported by Conformity, see here.

This rule can help you work with the AWS Well-Architected Framework.

This rule resolution is part of the Conformity Security & Compliance tool for AWS.

Security

Allowing unrestricted inbound/ingress access to Amazon EC2 instances on uncommon TCP/UDP ports can increase opportunities for malicious activities such as hacking, data capture, and all kinds of attacks (brute-force attacks, Man-in-the-Middle attack, and Denial-of-Service attacks).

Audit

To determine if your Amazon EC2 security groups allow unrestricted ingress access on uncommon TCP/UDP ports, perform the following operations:

Using AWS Console

01 Sign in to the AWS Management Console.

02 Navigate to Amazon EC2 console at https://console.aws.amazon.com/ec2/.

03 In the navigation panel, under Network & Security, choose Security Groups.

04 Select the Amazon EC2 security group that you want to examine.

05 Choose the Inbound rules tab from the console bottom panel to access the inbound rules created for the selected group.

06 Check the configuration value available in the Source column for any inbound/ingress rules with uncommon ports (other than the ones listed in the rule description). If one or more rules have the Source value set to 0.0.0.0/0 or ::/0(i.e.**Anywhere), the selected Amazon EC2 security group allows unrestricted traffic to uncommon ports, therefore the access to the associated EC2 instance(s) is not secured.

07 Repeat steps no. 4 – 6 for each EC2 security group available within the current AWS region.

08 Change the AWS cloud region from the navigation bar and repeat the audit process for other regions.

Using AWS CLI

01 Run describe-security-groups command (OSX/Linux/UNIX) with predefined filters to expose the ID of each Amazon EC2 security group that allows unrestricted inbound access to all IPv4 addresses (i.e. 0.0.0.0/0). Replace the --filters parameter value with the Name=ip-permission.ipv6-cidr,Values='::/0' to expose the security groups that allow unrestricted inbound access to all IPv6 addresses (::/0): 

aws ec2 describe-security-groups
  --region us-east-1
  --filters Name=ip-permission.cidr,Values='0.0.0.0/0'
  --output table
  --query 'SecurityGroups[*].GroupId'

02 If the describe-security-groups command does not produce an output, there are no security groups that allow unrestricted inbound access in the selected AWS region. Otherwise, the command output should return a table with the requested security group ID(s): 

--------------------------
| DescribeSecurityGroups |
+------------------------+
|  sg-01234abcd1234abcd  |
|  sg-0abcd1234abcd1234  |
+------------------------+

03 Run describe-security-groups command (OSX/Linux/UNIX) using custom query filters to list all the inbound/ingress rules defined for the selected EC2 security group: 

aws ec2 describe-security-groups
  --region us-east-1
  --group-ids sg-01234abcd1234abcd
  --query 'SecurityGroups[*].IpPermissions[]'

04 The command output should return the requested configuration information: 

[
	{
		"FromPort": 8040,
		"IpProtocol": "tcp",
		"IpRanges": [
			{
				"CidrIp": "0.0.0.0/0"
			}
		],
		"Ipv6Ranges": [
			{
				"CidrIpv6": "::/0"
			}
		],
		"PrefixListIds": [],
		"ToPort": 8040,
		"UserIdGroupPairs": []
	}
]

To identify any uncommon TCP/UDP ports, check the "FromPort" and "ToPort" attributes values. If one or more rules returned by the describe-security-groups command output are using uncommon ports (other than the ones listed in the rule description), the selected Amazon EC2 security group allows unrestricted traffic to uncommon ports, therefore the access to the associated EC2 instance(s) is not secured.

05 Repeat steps no. 3 and 4 for each EC2 security group available in the selected AWS region.

06 Change the AWS cloud region by updating the --region command parameter value and repeat steps no. 1 – 5 to perform the audit process for other regions.

Remediation / Resolution

To update the inbound rule configuration for your Amazon EC2 security groups in order to restrict access to trusted entities only (i.e. authorized IP addresses and IP ranges, or other security groups), perform the following operations:

Using AWS CloudFormation

01 CloudFormation template (JSON): 

{
	"AWSTemplateFormatVersion":"2010-09-09",
	"Description":"Allow inbound access on uncommon ports to trusted entities only",
	"Resources":{
		"CustomSecurityGroup" : {
			"Type" : "AWS::EC2::SecurityGroup",
			"Properties" : {
			"GroupDescription" : "Custom security group",
			"GroupName" : "custom-security-group",
			"VpcId" : "vpc-1234abcd",
			"SecurityGroupIngress" : [{
				"IpProtocol" : "tcp",
				"FromPort" : 8040,
				"ToPort" : 8040,
				"CidrIp" : "10.0.0.35/32"
			}],
			"SecurityGroupEgress" : [{
				"IpProtocol" : "-1",
				"FromPort" : 0,
				"ToPort" : 65535,
				"CidrIp" : "0.0.0.0/0"
			}]
			}
		}
	}
}

02 CloudFormation template (YAML): 

AWSTemplateFormatVersion: '2010-09-09'
    Description: Allow inbound access on uncommon ports to trusted entities only
    Resources:
        CustomSecurityGroup:
        Type: AWS::EC2::SecurityGroup
        Properties:
            GroupDescription: Custom security group
            GroupName: custom-security-group
            VpcId: vpc-1234abcd
            SecurityGroupIngress:
            - IpProtocol: tcp
            FromPort: 8040
            ToPort: 8040
            CidrIp: 10.0.0.35/32
            SecurityGroupEgress:
            - IpProtocol: "-1"
            FromPort: 0
            ToPort: 65535
            CidrIp: 0.0.0.0/0

Using Terraform (AWS Provider)

01 Terraform configuration file (.tf): 

terraform {
	required_providers {
		aws = {
			source  = "hashicorp/aws"
			version = "~> 3.27"
		}
	}

	required_version = ">= 0.14.9"
}

provider "aws" {
	profile = "default"
	region  = "us-east-1"
}

resource "aws_security_group" "security-group" {
	name        = "custom-security-group"
	description = "Custom security group"
	vpc_id      = "vpc-1234abcd"

	# Allow inbound access on uncommon ports to trusted IPs/IP ranges only
	ingress {
		from_port        = 8040
		to_port          = 8040
		protocol         = "tcp"
		cidr_blocks      = ["10.0.0.35/32"]
	}

	egress {
		from_port        = 0
		to_port          = 0
		protocol         = "-1"
		cidr_blocks      = ["0.0.0.0/0"]
	}

}

Using AWS Console

01 Sign in to the AWS Management Console.

02 Navigate to Amazon EC2 console at https://console.aws.amazon.com/ec2.

03 In the navigation panel, under Network & Security, choose Security Groups.

04 Select the Amazon EC2 security group that you want to reconfigure (see Audit section part I to identify the right resource).

05 Select the Inbound rules tab from the console bottom panel and choose Edit inbound rules.

06 On the Edit inbound rules configuration page, change the traffic source for the inbound rule that allows unrestricted access through uncommon TCP/UDP ports, by performing one of the following actions:

  1. Select My IP from the Source dropdown list to allow inbound traffic only from your current IP address.
  2. Select Custom from the Source dropdown list and enter one of the following options based on your access requirements: The static IP address of the permitted host in CIDR notation (e.g. 10.0.0.35/32). The IP address range of the permitted network/subnetwork in CIDR notation, for example 10.0.5.0/24. The name or ID of another security group available in the same AWS cloud region.
  3. Choose Save rules to apply the configuration changes.

07 Repeat steps no. 4 – 6 to reconfigure other EC2 security groups that allow unrestricted access on uncommon TCP/UDP ports.

08 Change the AWS cloud region from the navigation bar and repeat the remediation process for other regions.

Using AWS CLI

01 Run revoke-security-group-ingress command (OSX/Linux/UNIX) using the ID of the Amazon EC2 security group that you want to reconfigure as the identifier parameter (see Audit section part II to identify the right resource), to remove the inbound rules that allow unrestricted access through uncommon TCP ports. Replace tcp with udp within the IpProtocol parameter value to remove the ingress rule that allows unrestricted access on uncommon UDP ports: 

aws ec2 revoke-security-group-ingress
  --region us-east-1
  --group-id sg-01234abcd1234abcd
  --ip-permissions IpProtocol=tcp,FromPort=8040,ToPort=8040,IpRanges=[{CidrIp="0.0.0.0/0"}],Ipv6Ranges=[{CidrIpv6="::/0"}]
  --query 'Return'

02 The command output should return true if the request succeeds. Otherwise, it should return an error: 

true

03 Run authorize-security-group-ingress command (OSX/Linux/UNIX) to add the inbound rule removed at the previous step with a different set of parameters in order to restrict access to trusted entities only (IP addresses, IP ranges, or security groups). To create and attach custom inbound/ingress rules to the selected Amazon EC2 security group based on your access requirements, use one of the following options (the command does not produce an output):

  1. Add an inbound rule that allows traffic from an authorized static IP address via TCP port 8040 (uncommon port), using CIDR notation (e.g. 10.0.0.35/32). Replace tcp with udp within the --protocol command parameter value for rules with uncommon UDP ports: 
    aws ec2 authorize-security-group-ingress
  --region us-east-1
  --group-id sg-01234abcd1234abcd
  --protocol tcp
  --port 8040
  --cidr 10.0.0.35/32
  2. Add an inbound/ingress rule that allows traffic from a trusted IP address range through TCP port 8040, using CIDR notation (for example, 10.0.5.0/24). Replace tcp with udp within the --protocol command parameter value for rules with uncommon UDP ports: 
    aws ec2 authorize-security-group-ingress
  --region us-east-1
  --group-id sg-01234abcd1234abcd
  --protocol tcp
  --port 8040
  --cidr 10.0.5.0/24
  3. Add an inbound rule that allows traffic from another security group (e.g. sg-01234123412341234) available in the same AWS cloud region via TCP port 8040. Replace tcp with udp within the --protocol command parameter value for rules with uncommon UDP ports: 
    aws ec2 authorize-security-group-ingress
  --region us-east-1
  --group-id sg-01234abcd1234abcd
  --protocol tcp
  --port 8040
  --source-group sg-01234123412341234

04 Repeat steps no. 1 – 3 to reconfigure other EC2 security groups that allow unrestricted access on uncommon TCP/UDP ports.

05 Change the AWS cloud region by updating the --region command parameter value and repeat steps no. 1 – 4 to perform the remediation process for other regions.

References

Publication date Jun 19, 2016

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