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Unrestricted ICMP Access

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Risk Level: Medium (should be achieved)
Rule ID: EC2-044

Check your Amazon EC2 security groups for inbound rules that allow unrestricted access (i.e. 0.0.0.0/0 or ::/0) to any hosts using ICMP and restrict the ICMP-based access to trusted IP addresses/IP ranges only in order to implement the Principle of Least Privilege (POLP) and reduce the attack surface. Internet Control Message Protocol (ICMP) is an error-reporting protocol that is typically used to troubleshoot TCP/IP networks by generating error messages for any issues with delivering IP packets. Even if ICMP is not a transport protocol, it can be used to exploit network vulnerabilities.

This rule can help you with the following compliance standards:

  • PCI
  • 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 ICMP access to your Amazon EC2 instances can increase opportunities for malicious activities such as Denial-of-Service (DoS) attacks, Smurf and Fraggle attacks.

Audit

To determine if your Amazon EC2 security groups allow unrestricted ICMP access, 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 Click inside the Filter security groups box located under the console top menu, choose Protocol, and select ICMP from the protocols list.

05 Select the security group that you want to examine and 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 the Protocol set to ICMP. 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 any hosts using ICMP, therefore the access to the associated EC2 instance(s) is not secured.

07 Repeat steps no. 5 and 6 for each EC2 security group returned as result at step no. 4.

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 and custom query filters to expose the ID of each Amazon EC2 security group that allows unrestricted traffic to any hosts using the ICMP protocol: 

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

02 The command output should return a table with the requested security group ID(s): 

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

If the describe-security-groups command does not produce an output, there are no security groups that allow unrestricted ICMP access in the selected AWS region. If the command output returns a table with one or more security group IDs, those Amazon EC2 security groups allow unrestricted traffic to any hosts using ICMP, therefore the access to the associated EC2 instance(s) is not secured.

03 Change the AWS cloud region by updating the --region command parameter value and repeat steps no. 1 and 2 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 ICMP-based 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":"Configure security group to restrict inbound ICMP-based access to trusted IP(s) only",
	"Resources":{
		"EC2SecurityGroup" : {
			"Type" : "AWS::EC2::SecurityGroup",
			"Properties" : {
			"GroupDescription" : "Allow ICMP-based access",
			"GroupName" : "custom-icmp-security-group",
			"VpcId" : "vpc-1234abcd",
			"SecurityGroupIngress" : [{
				"IpProtocol" : "icmp",
				"FromPort" : -1,
				"ToPort" : -1,
				"CidrIp" : "10.0.0.5/32"
			}],
			"SecurityGroupEgress" : [{
				"IpProtocol" : "-1",
				"FromPort" : 0,
				"ToPort" : 65535,
				"CidrIp" : "0.0.0.0/0"
			}]
			}
		}
	}
}

02 CloudFormation template (YAML): 

AWSTemplateFormatVersion: '2010-09-09'
	Description: Configure security group to restrict inbound ICMP-based access to trusted IP(s) only
	Resources:
		EC2SecurityGroup:
		Type: AWS::EC2::SecurityGroup
		Properties:
			GroupDescription: Allow ICMP-based access
			GroupName: custom-icmp-security-group
			VpcId: vpc-1234abcd
			SecurityGroupIngress:
			- IpProtocol: icmp
			FromPort: -1
			ToPort: -1
			CidrIp: 10.0.0.5/32
			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" "custom-security-group" {
	name        = "custom-icmp-security-group"
	description = "Allow ICMP-based access"
	vpc_id      = "vpc-1234abcd"

	# Configure ingress rule to restrict inbound ICMP-based access to trusted IPs only
	ingress {
		from_port        = -1
		to_port          = -1
		protocol         = "icmp"
		cidr_blocks      = ["10.0.0.5/32"]
	}

	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 traffic to any hosts using ICMP, 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. 10.0.0.5/32).
    • 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 ICMP access.

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 traffic to any hosts using Internet Control Message Protocol (ICMP): 

aws ec2 revoke-security-group-ingress
  --region us-east-1
  --group-id sg-01234abcd1234abcd
  --ip-permissions IpProtocol=icmp,FromPort=-1,ToPort=-1,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 ICMP 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 ICMP traffic from an authorized static IP address using CIDR notation (e.g. 10.0.0.5/32). A value of -1 for the --port command parameter indicates all ICMP codes: 
    aws ec2 authorize-security-group-ingress
  --region us-east-1
  --group-id sg-01234abcd1234abcd
  --protocol icmp
  --port -1
  --cidr 10.0.0.5/32
  2. Add an inbound/ingress rule that allows all ICMP traffic from a trusted IP address range using CIDR notation (for example, 10.0.5.0/24): 
    aws ec2 authorize-security-group-ingress
  --region us-east-1
  --group-id sg-01234abcd1234abcd
  --protocol icmp
  --port -1
  --cidr 10.0.5.0/24
  3. Add an inbound rule that allows all ICMP traffic from another security group (e.g. sg-01234123412341234) available in the same AWS cloud region: 
    aws ec2 authorize-security-group-ingress
  --region us-east-1
  --group-id sg-01234abcd1234abcd
  --protocol icmp
  --port -1
  --source-group sg-01234123412341234

04 Repeat steps no. 1 – 3 to reconfigure other EC2 security groups that allow unrestricted ICMP access.

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 23, 2016

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