AWS Firewall Construct

A simple AWS VPC Firewall with one stateless rule and one stateful rule to meet the AWS Config Network Firewall Conformance.

Stateful rules group can be further extend with Suricata rules as text file

Example stateless rule group

Allows only TCP:80 and TCP:443 by adding NetworkFirewallRulesBuilder.statelessRulesAllowedPorts(stack) to the NetworkFirewallDistributedConstruct()

Stateful rule group

Builds from a rule text file using NetworkFirewallRulesBuilder.statefulRulesSourcePropertyFromFile(stack,["./test/rules.txt"]) to the NetworkFirewallDistributedConstruct()

Example use case

1. Create a new folder network-firewall in the same level as cdk-construct
1. Initialize a CDK app using command cdk new app --language=typescript
1. Update cdk.json with environment context, for example
``
{
"app": "npx ts-node --prefer-ts-exts bin/network-firewall.ts",
[...]]
"context": {
[...]]
"staging":{
"vpcId": "",
"subnets": [
"",
"",
""
]
},
"production":{
"vpcId": "",
"subnets": [
"",
"",
""
]
}
}
}
`
2. In the bin/network-firewall.ts

`
#!/usr/bin/env node
import 'source-map-support/register';
import * as cdk from 'aws-cdk-lib';
import { NetworkFirewallStack } from '../lib/network-firewall-stack';

const app = new cdk.App();

const runtimeEnv = app.node.tryGetContext('config');
const context = app.node.tryGetContext(app.node.tryGetContext('config'));

const readConfig = (context:{[name:string]:any}, key:string):any => {
if(!context[key])
throw new Error(${key} not found or is empty);

if(typeof(context[key]) === "string" && context[key].trim().length === 0 )
throw new Error(${key} not found or is empty);

if(Array.isArray(context[key]) && context[key].length < 1)
throw new Error(${key} not found or is empty);

return context[key];
}

new NetworkFirewallStack(app, 'NetworkFirewallStack', {
vpcId: readConfig(context,"vpcId"),
subnets: readConfig(context,"subnets"),
environmentName: runtimeEnv,
// needs the account and region for the Vpc lookup
env: {
region: process.env.CDK_DEFAULT_REGION,
account: process.env.CDK_DEFAULT_ACCOUNT,
},
});
`

4. Create a Suricata text file in lib/rules.txt as below. More examples can be found in https://suricata.readthedocs.io/en/suricata-6.0.2/rules/intro.html

`
pass ip 10.1.0.0/16 any -> 10.0.0.0/16 any (sid:100;)
drop ip any any <> any any (sid:101;)
alert tcp any any -> 1.1.1.1/32 80 (sid:102;msg:"example message";)
drop tls $HOME_NET any -> $EXTERNAL_NET any (tls.sni; content:"example.com"; startswith; nocase; endswith; msg:"matching TLS denylisted FQDNs"; priority:1; flow:to_server, established; sid:103; rev:1;)
drop http $HOME_NET any -> $EXTERNAL_NET any (http.host; content:"example.com"; startswith; endswith; msg:"matching HTTP denylisted FQDNs"; priority:1; flow:to_server, established; sid:104; rev:1;)
`

3. In the lib/network-firewall-stack.ts
`
import * as cdk from 'aws-cdk-lib';
import { Construct } from 'constructs';
import * as fwconstruct from '../../cdk-constructs/firewall-distributed-vpc'

export interface NetworkFirewallStackProps extends cdk.StackProps{
readonly environmentName: string,
readonly vpcId: string,
readonly subnets: string[]
}

export class NetworkFirewallStack extends cdk.Stack {
constructor(scope: Construct, id: string, props?: cdk.StackProps) {
super(scope, id, props);
const vpc:cdk.aws_ec2.IVpc = cdk.aws_ec2.Vpc.fromLookup(this,fw-${props.environmentName}-Vpc,
{
vpcId: props.vpcId
});

var index=0;
const subnetList:cdk.aws_ec2.ISubnet[] = props.subnets.map((subnet)=>cdk.aws_ec2.Subnet.fromSubnetId(this, fw-${props.environmentName}-${index++}, subnet));

new fwconstruct.FirewallDistributedVpc(this,'fw',{
vpc: vpc,
subnetList:subnetList
})
.addStatelessRuleGroup(
fwconstruct.NetworkFirewallRulesBuilder.statelessRulesAllowedPorts(this)
)
.addStatefulRules(
fw.NetworkFirewallRulesBuilder.statefulRulesSourcePropertyFromFile(stack,["./lib/rules.txt"])
)
.buildFirewall();

}
}
`
4. Update the package.json with the context

`
{
"name": "network-firewall",
"version": "0.1.0",
"bin": {
"network-firewall": "bin/network-firewall.js"
},
"scripts": {
[...]
"cdk-deploy-staging": "tsc && cdk deploy -c config=staging",
"cdk-deploy-production": "tsc && cdk deploy -c config=production"
}
[...]
}
`
5. Deploy with npm run cdk-deploy-staging or npm run cdk-deploy-production

Validate with Config Conformance Pack

To ensure network firewall conformance, deploy the conformance pack using Network Firewall Conformance Pack.

Check the config rule conformation

1. Get the rule names
`
% aws configservice describe-config-rules --query 'ConfigRules[*].ConfigRuleName'
[
"netfw-policy-default-action-fragment-packets-conformance-pack-ilk1uyn2w",
"netfw-policy-default-action-full-packets-conformance-pack-ilk1uyn2w",
"netfw-policy-rule-group-associated-conformance-pack-ilk1uyn2w",
"netfw-stateless-rule-group-not-empty-conformance-pack-ilk1uyn2w"
]
`
2. Query the compliance details
`
aws configservice get-compliance-details-by-config-rule --config-rule-name netfw-policy-default-action-fragment-packets-conformance-pack-ilk1uyn2w --query 'EvaluationResults[*].ComplianceType'
[
"COMPLIANT"
]
``