Unrestricted RPC Access

01 Sign in to the AWS Management Console.

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

03 In the left navigation panel, under NETWORK & SECURITY section, choose Security Groups.

04 Click inside the attributes filter box located under the dashboard top menu and select the following options from the dropdown list:

1. Choose Protocol and select TCP from the protocols list.
2. Choose Port Range, type 135 for the port number and press Enter.

05 Select an EC2 security group returned as result.

06 Select the Inbound tab from the dashboard bottom panel.

07 Verify the value available in the Source column for any inbound/ingress rules with the Port Range set to 135. If one or more rules have the source set to 0.0.0.0/0 or ::/0 (Anywhere), the selected security group allows unrestricted data traffic on port 135, therefore the Remote Procedure Call (RPC) access to the associated EC2 instance(s) is not secured.

08 Repeat steps no. 5 – 7 to verify the rest of the EC2 security groups returned as result at step no. 4.

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

01 Run describe-security-groups command (OSX/Linux/UNIX) using the necessary filters to expose the security groups that have ingress rules that allow RPC traffic (TCP port 135) from all addresses (0.0.0.0/0 or ::/0):

aws ec2 describe-security-groups
	--region us-east-1
	--filters Name=ip-permission.from-port,Values=135 Name=ip-permission.to-port,Values=135 Name=ip-permission.cidr,Values='0.0.0.0/0'
	--query 'SecurityGroups[*].{Name:GroupName}'

aws ec2 describe-security-groups
	--region us-east-1
	--filters Name=ip-permission.from-port,Values=135 Name=ip-permission.to-port,Values=135 Name=ip-permission.ipv6-cidr,Values='::/0'
	--query 'SecurityGroups[*].{Name:GroupName}'

02 The command output should return an array with the requested information. If the command does not return any output, there are no EC2 security groups that allow unrestricted RPC access, otherwise it should return the name of the security group(s) that match filter criteria, as shown in the following example:

[
    {
        "Name": "MSServerSecurityGroup"
    },
    {
        "Name": "MyWebEC2SecurityGroup"
    }
]

03 Repeat step no. 1 and 2 to perform the audit process for other AWS regions.

01 Sign in to the AWS Management Console.

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

03 In the navigation panel, under NETWORK & SECURITY section, choose Security Groups.

04 Select the appropriate security group (see Audit section to identify the right one(s)).

05 Select the Inbound tab from the dashboard bottom panel and click the Edit button.

06 In the Edit inbound rules dialog box, change the traffic Source for any inbound rules that allow unrestricted access through TCP port 135 by performing one of the following actions:

1. Select My IP from the Source dropdown list to allow inbound traffic only from your machine (from your 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/Elastic IP address of the permitted host with the suffix set to /32, e.g. 51.134.56.198/32.
   • The IP address range of the permitted hosts in CIDR notation, for example 51.134.56.198/24.
   • The name or ID of another security group available in the same AWS region.

07 Click Save to apply the changes.

08 Repeat steps no. 4 – 7 to update other EC2 security groups that allow unrestricted RPC access.

09 Change the AWS region from the navigation bar and repeat the process for other regions.

01 First, run revoke-security-group-ingress command (OSX/Linux/UNIX) to remove the inbound rule(s) that allow unrestricted access through TCP port 135, from the selected EC2 security group (the command does not return an output):

aws ec2 revoke-security-group-ingress
	--region us-east-1
	--group-name MSServerSecurityGroup
	--protocol tcp
	--port 135
	--cidr 0.0.0.0/0

02 Run authorize-security-group-ingress command (OSX/Linux/UNIX) to add the inbound rules removed at the previous step with a different set of parameters in order to restrict Remote Procedure Call (RPC) access to specific entities. To add custom inbound/ingress rules to the selected security group, use one of the following options (the command does not produce an output):

1. Add an inbound rule that allows RPC access to the specific static IP/Elastic IP address of the permitted host via port 135:
   aws ec2 authorize-security-group-ingress
   	--region us-east-1
   	--group-name MSServerSecurityGroup
   	--protocol tcp
   	--port 135
   	--cidr 54.164.53.205/32
   

2. Add an inbound rule that allows RPC access to the IP address range of the permitted hosts via port 135:
   aws ec2 authorize-security-group-ingress
   	--region us-east-1
   	--group-name MSServerSecurityGroup
   	--protocol tcp
   	--port 135
   	--cidr 54.164.53.205/24
   

3. Add an inbound rule that allows RPC access to another EC2 security group in the same AWS region via port 135:
   aws ec2 authorize-security-group-ingress
   	--region us-east-1
   	--group-name MSServerSecurityGroup
   	--protocol tcp
   	--port 135
   	--source-group MyWebAppSecurityGroup
   

03 Repeat step no. 1 and 2 to update other EC2 security groups that allow unrestricted RPC access using AWS CLI.

04 Repeat steps no. 1 - 3 to implement the entire process for other AWS regions.