Examples of stateful rules for Network Firewall - AWS Network Firewall
Allow trafficBlock trafficDomain listLoggingManaging rule evaluation orderRule with variablesRule with IP set referenceStandard stateful rule groups

Examples of stateful rules for Network Firewall

This section lists examples of Suricata compatible rules that could be used with AWS Network Firewall.

Note

Examples are not intended to be used in your Network Firewall configuration exactly as they are listed.

The examples provide general information and sample rule specifications for common use cases. Before using any rule from these examples or elsewhere, test and adjust it carefully to be sure that it fits your needs. It's your responsibility to ensure that each rule that you use is suited to your specific use case and functioning the way that you want it to.

Allow traffic

Note

Before using any example rule, test and adapt it to your needs.

The examples in this section contain examples that allow specified traffic.

Allow access to any ssm. Server Name Indication (SNI) ending with .amazonaws.com

Allows access to any domain that begins with ssm. and ends with .amazonaws.com (http://amazonaws.com/).

pass tls $HOME_NET any -> $EXTERNAL_NET any (tls.sni; content:"ssm."; ssl_state:client_hello; startswith; content:".amazonaws.com"; endswith; nocase; flow: to_server; sid:202308311;)
JA3 hash

This rule allows outbound access using a specific JA3 hash

pass tls $HOME_NET any -> $EXTERNAL_NET any (msg:"Only allow Curl 7.79.1 JA3"; ja3.hash; content:"27e9c7cc45ae47dc50f51400db8a4099"; sid:12820009;)
Outbound requests to checkip.amazonaws.com

These rules only allow outbound requests to the SNI checkip.amazonaws.com (http://checkip.amazonaws.com/) if the server certificate issuer is also Amazon. Requires that your firewall policy uses strict order rule evaluation order.

alert tls $HOME_NET any -> $EXTERNAL_NET 443 (tls.sni; content:"checkip.amazonaws.com"; ssl_state:client_hello; endswith; nocase; xbits:set, allowed_sni_destination_ips, track ip_dst, expire 3600; noalert; sid:238745;)
pass tcp $HOME_NET any -> $EXTERNAL_NET 443 (xbits:isset, allowed_sni_destination_ips, track ip_dst; flow: stateless; sid:89207006;)
pass tls $EXTERNAL_NET 443 -> $HOME_NET any (tls.cert_issuer; content:"Amazon"; msg:"Pass rules do not alert"; xbits:isset, allowed_sni_destination_ips, track ip_src; sid:29822;)
reject tls $EXTERNAL_NET 443 -> $HOME_NET any (tls.cert_issuer; content:"="; nocase; msg:"Block all other cert issuers not allowed by sid:29822"; sid:897972;)
Outbound SSH/SFTP servers with AWS_SFTP banner

These rules only allow outbound access to SSH/SFTP servers that have a banner that includes AWS_SFTP, which is the banner for AWS Transfer Family servers. To check for a different banner, replace AWS_SFTP with the banner you want to check for.

pass tcp $HOME_NET any -> $EXTERNAL_NET 22 (flow:stateless; sid:2221382;)
pass ssh $EXTERNAL_NET 22 -> $HOME_NET any (ssh.software; content:"AWS_SFTP"; flow:from_server; sid:217872;)
drop ssh $EXTERNAL_NET 22 -> $HOME_NET any (ssh.software; content:!"@"; pcre:"/[a-z]/i"; msg:"Block unauthorized SFTP/SSH."; flow: from_server; sid:999217872;)
Send DNS query including .amazonaws.com to external DNS servers

This rule allows any DNS query for domain names ending in .amazonaws.com (http://amazonaws.com/) to be sent to external DNS servers.

pass dns $HOME_NET any -> $EXTERNAL_NET any (dns.query; dotprefix; content:".amazonaws.com"; endswith; nocase; msg:"Pass rules do not alert"; sid:118947;)

Block traffic

Note

Before using any example rule, test and adapt it to your needs.

The examples in this section contain examples that block specified traffic.

Connections using TLS versions 1.0 or 1.1

This rule blocks connections using TLS version 1.0 or 1.1.

reject tls any any -> any any (msg:"TLS 1.0 or 1.1"; ssl_version:tls1.0,tls1.1; sid:2023070518;)
Multiple CIDR ranges

This rule blocks outbound access to multiple CIDR ranges in a single rule.

drop ip $HOME_NET any-> [10.10.0.0/16,10.11.0.0/16,10.12.0.0/16] (msg:"Block traffic to multiple CIDRs"; sid:278970;)
Multiple SNIs

This rule blocks multiple SNIs with a single rule.

reject tls $HOME_NET any -> $EXTERNAL_NET any (tls.sni; ssl_state:client_hello; pcre:"/(example1\.com|example2\.com)$/i"; flow: to_server; msg:"Domain blocked"; sid:1457;)
Multiple high-risk destination outbound ports

This rule blocks multiple high-risk destination outbound ports in a single rule.

drop ip $HOME_NET any -> $EXTERNAL_NET [1389,53,4444,445,135,139,389,3389] (msg:"Deny List High Risk Destination Ports"; sid:278670;)
Outbound HTTP HOST

This rule blocks outbound HTTP connections that have an IP address in the HTTP HOST header.

reject http $HOME_NET any -> $EXTERNAL_NET any (http.host; content:"."; pcre:"/^(?:[0-9]{1,3}\.){3}[0-9]{1,3}$/"; msg:"IP in HTTP HOST Header (direct to IP, likely no DNS resolution first)"; flow:to_server; sid:1239847;)
Outbound TLS with IP in SNI

This rule blocks outbound TLS connections with an IP address in the SNI.

reject tls $HOME_NET any -> $EXTERNAL_NET any (tls.sni; ssl_state:client_hello; content:"."; pcre:"/^(?:[0-9]{1,3}\.){3}[0-9]{1,3}$/"; msg:"IP in TLS SNI (direct to IP, likely no DNS resolution first)"; flow:to_server; sid:1239848;)
Any IP protocols other than TCP, UDP, and ICMP

This rule silently blocks any IP protocols other than TCP, UDP, and ICMP.

drop ip any any-> any any (noalert; ip_proto:!TCP; ip_proto:!UDP; ip_proto:!ICMP; sid:21801620;)
SSH non-standard ports

This rule blocks the use of the SSH protocol on non-standard ports.

reject ssh $HOME_NET any -> $EXTERNAL_NET !22 (msg:"Block use of SSH protocol on non-standard port"; flow: to_server; sid:2171010;)
TCP/22 servers non-SSH

This rule blocks the use of TCP/22 servers that aren't using the SSH protocol.

reject tcp $HOME_NET any -> $EXTERNAL_NET 22 (msg:"Block TCP/22 servers that are not SSH protocol"; flow: to_server; app-layer-protocol:!ssh; sid:2171009;)

Domain list

Note

Before using any example rule, test and adapt it to your needs.

Deny list example JSON, rule group creation, and generated Suricata rules

The following JSON shows an example rule definition for a Network Firewall domain list rule group that specifies a deny list.

{
    "RulesSource": {
        "RulesSourceList": {
            "Targets": [
                "evil.com"
            ],
            "TargetTypes": [
                 "TLS_SNI",
                 "HTTP_HOST"
             ],
             "GeneratedRulesType": "DENYLIST"
        }
    }
}

To use the Network Firewall rule specification, we save the JSON to a local file domainblock.example.json, and then create the rule group in the following CLI command: 

aws network-firewall create-rule-group --rule-group-name "RuleGroupName" --type STATEFUL --rule-group file://domainblock.example.json --capacity 1000

The following Suricata rules listing shows the rules that Network Firewall creates for the above deny list specification.

drop tls $HOME_NET any -> $EXTERNAL_NET any (tls.sni; content:"evil.com"; ssl_state:client_hello; startswith; nocase; endswith; msg:"matching TLS denylisted FQDNs"; priority:1; flow:to_server, established; sid:1; rev:1;)
drop http $HOME_NET any -> $EXTERNAL_NET any (http.host; content:"evil.com"; startswith; endswith; msg:"matching HTTP denylisted FQDNs"; priority:1; flow:to_server, established; sid:2; rev:1;)
HTTP allow list example JSON and generated Suricata rules

The following JSON shows an example rule definition for a Network Firewall domain list rule group that specifies an HTTP allow list. The . before the domain name in .amazon.com is the wildcard indicator in Suricata.

{
    "RulesSource": {
        "RulesSourceList": {
            "Targets": [
                ".amazon.com",
                "example.com"
            ],
            "TargetTypes": [
                "HTTP_HOST"
            ],
            "GeneratedRulesType": "ALLOWLIST"
        }
    }
}

The following Suricata rules listing shows the rules that Network Firewall creates for the above allow list specification.

pass http $HOME_NET any -> $EXTERNAL_NET any (http.host; dotprefix; content:".amazon.com"; endswith; msg:"matching HTTP allowlisted FQDNs"; priority:1; flow:to_server, established; sid:1; rev:1;)
pass http $HOME_NET any -> $EXTERNAL_NET any (http.host; content:"example.com"; startswith; endswith; msg:"matching HTTP allowlisted FQDNs"; priority:1; flow:to_server, established; sid:2; rev:1;)
drop http $HOME_NET any -> $EXTERNAL_NET any (http.header_names; content:"|0d 0a|"; startswith; msg:"not matching any HTTP allowlisted FQDNs"; priority:1; flow:to_server, established; sid:3; rev:1;)
TLS allow list example JSON and generated Suricata rules

The following JSON shows an example rule definition for a Network Firewall domain list rule group that specifies a TLS allow list.

{
    "RulesSource": {
        "RulesSourceList": {
            "Targets": [
                ".amazon.com",
                "example.com"
            ],
            "TargetTypes": [
                "TLS_SNI"
            ],
            "GeneratedRulesType": "ALLOWLIST"
        }
    }
}

The following Suricata rules listing shows the rules that Network Firewall creates for the above allow list specification.

pass tls $HOME_NET any -> $EXTERNAL_NET any (tls.sni; dotprefix; content:".amazon.com"; ssl_state:client_hello; nocase; endswith; msg:"matching TLS allowlisted FQDNs"; priority:1; flow:to_server, established; sid:1; rev:1;)
pass tls $HOME_NET any -> $EXTERNAL_NET any (tls.sni; content:"example.com"; ssl_state:client_hello; startswith; nocase; endswith; msg:"matching TLS allowlisted FQDNs"; priority:1; flow:to_server, established; sid:2; rev:1;)
drop tls $HOME_NET any -> $EXTERNAL_NET any (msg:"not matching any TLS allowlisted FQDNs"; priority:1; flow:to_server, established; sid:3; rev:1;)
Block traffic from $EXTERNAL_NET to $HOME_NET, allow outbound domain filtering

These rules block all unsolicited traffic from $EXTERNAL_NET to $HOME_NET while still allowing outbound domain filtering.

reject tls any any -> any any (msg:"Vulnerable versions of TLS"; ssl_version:tls1.0,tls1.1; sid:2023070518;)

Logging

Note

Before using any example rule, test and adapt it to your needs.

The examples in this section demonstrate ways to log traffic. To log traffic, you must configure logging for your firewall. For information about logging Network Firewall traffic, see Logging and monitoring in AWS Network Firewall.

Log traffic direction in default-deny policy

Can be used at the end of a default-deny policy to accurately log the direction of denied traffic. These rules help you to make it clear in the logs who the client is and who the server is in the connection.

reject tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"Default Egress TCP block to server"; flow:to_server; sid:202308171;)
drop udp $HOME_NET any -> $EXTERNAL_NET any (msg:"Default Egress UDP block";sid:202308172;)
drop icmp $HOME_NET any -> $EXTERNAL_NET any (msg:"Default Egress ICMP block";sid:202308177;)
drop tcp $EXTERNAL_NET any -> $HOME_NET any (msg:"Default Ingress block to server"; flow:to_server; sid:20230813;)
drop udp $EXTERNAL_NET any -> $HOME_NET any (msg:"Default Ingress UDP block"; sid:202308174;)
drop icmp $EXTERNAL_NET any -> $HOME_NET any (msg:"Default Ingress ICMP block"; sid:202308179;)
Log traffic to an allowed SNI.

These rules log traffic to an allowed SNI. Requires your policy to use strict order rule evaluation order.

alert tls $HOME_NET any -> $EXTERNAL_NET any (tls.sni; content:".example.com"; ssl_state:client_hello; dotprefix; endswith; nocase; msg:"example.com (http://example.com/) allowed by rule 202307052"; sid:202307051;)
pass tls $HOME_NET any -> $EXTERNAL_NET any (tls.sni; content:".example.com"; ssl_state:client_hello; dotprefix; endswith; nocase; sid:202307052;)

Managing rule evaluation order

Note

Before using any example rule, test and adapt it to your needs.

The examples in this section demonstrate ways to modify evaluation behavior by modifying rule evaluation order in Suricata compatible rules. Network Firewall recommends using strict order so that you can have control over the way your rules are processed for evaulation. For information about managing rule evaluation order, see Evaluation order for stateful rule groups.

Allow HTTP traffic to specific domains:

Default action order

drop tcp $HOME_NET any -> $EXTERNAL_NET 80 (msg:"Drop established TCP:80"; flow: from_client,established; sid:172190; priority:5; rev:1;)
pass http $HOME_NET any -> $EXTERNAL_NET 80 (http.host; dotprefix; content:".example.com"; endswith; msg:"Allowed HTTP domain"; priority:10; sid:172191; rev:1;)
pass tcp $HOME_NET any -> $EXTERNAL_NET 22 (msg:"Allow TCP 22"; sid:172192; rev:1;)
drop tcp $HOME_NET any -> $EXTERNAL_NET !80 (msg:"Drop All non-TCP:80";  sid:172193; priority:2; rev:1;)

Strict order

pass http $HOME_NET any -> $EXTERNAL_NET 80 (http.host; dotprefix; content:".example.com"; endswith; msg:"Allowed HTTP domain"; sid:172191; rev:1;)
pass tcp $HOME_NET any -> $EXTERNAL_NET 22 (msg:"Allow TCP 22"; sid:172192; rev:1;)

Allow HTTP traffic to specific domains only:

Default action order

pass http $HOME_NET any -> $EXTERNAL_NET 80 (http.host; dotprefix; content:".example.com"; endswith; msg:"Allowed HTTP domain"; priority:1; sid:102120; rev:1;)
pass http $HOME_NET any -> $EXTERNAL_NET 80 (http.host; dotprefix; content:".mydomain.test"; endswith; msg:"Allowed HTTP domain"; priority:1; sid:102121; rev:1;)
drop http $HOME_NET any -> $EXTERNAL_NET 80 (msg:"Drop HTTP traffic"; priority:1; sid:102122; rev:1;)

Strict order

pass http $HOME_NET any -> $EXTERNAL_NET 80 (http.host; dotprefix; content:".example.com"; endswith; msg:"Allowed HTTP domain"; sid:102120; rev:1;)
pass http $HOME_NET any -> $EXTERNAL_NET 80 (http.host; dotprefix; content:".mydomain.test"; endswith; msg:"Allowed HTTP domain"; sid:102121; rev:1;)

Allow HTTP traffic to specific domains only and deny all other IP traffic:

Default action order

pass http $HOME_NET any -> $EXTERNAL_NET 80 (http.host; dotprefix; content:".example.com"; endswith; msg:"Allowed HTTP domain"; priority:1; sid:892120; rev:1;)
drop tcp $HOME_NET any -> $EXTERNAL_NET 80 (msg:"Drop established non-HTTP to TCP:80"; flow: from_client,established; sid:892191; priority:5; rev:1;)
drop ip $HOME_NET any <> $EXTERNAL_NET any (msg: "Drop non-TCP traffic."; ip_proto:!TCP;sid:892192; rev:1;)
drop tcp $HOME_NET any -> $EXTERNAL_NET !80 (msg:"Drop All non-TCP:80"; sid:892193; priority:2; rev:1;)

Strict order

pass http $HOME_NET any -> $EXTERNAL_NET 80 (http.host; dotprefix; content:".example.com"; endswith; msg:"Allowed HTTP domain"; sid:892120; rev:1;)
pass tcp $HOME_NET any <> $EXTERNAL_NET 80 (flow:not_established; sid:892191; rev:1;)

Rule with variables

Note

Before using any example rule, test and adapt it to your needs.

The following JSON defines an example Suricata compatible rule group that uses the variables HTTP_SERVERS and HTTP_PORTS, with the variable definitions provided in the rule group declaration. 

{
"RuleVariables": {
    "IPSets": {
        "HTTP_SERVERS": {
            "Definition": [
                "10.0.2.0/24",
                "10.0.1.19"
            ]
        }
    },
    "PortSets": {
        "HTTP_PORTS": {
            "Definition": ["80", "8080"]
        }
    }
},
"RulesSource": {
    "RulesString": "alert tcp $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:\".htpasswd access attempt\"; flow:to_server,established; content:\".htpasswd\"; nocase; sid:210503; rev:1;)"
}
}

The variable EXTERNAL_NET is a Suricata standard variable that represents the traffic destination. For more information, see https://suricata.readthedocs.io/en/suricata-6.0.9/rules/intro.html#ports-source-and-destination.

Rule with IP set reference

Note

Before using any example rule, test and adapt it to your needs.

To reference a prefix list in your rule group, specify a IP set variable name and associate it with the prefix list's Amazon Resource Name (ARN). Then, specify the variable in one or more of your rules, prefacing the variable with @, such as @IP_Set_Variable. The variable represents the IPv4 prefix list that you are referencing. For more information about using IP set references, see Referencing Amazon VPC prefix lists.

The following example shows a Suricata compatible rule that uses an IP set reference variable @BETA as the source port in RulesString. To use an IP set reference in your rule, you must use an @ in front of the IP set variable name, such as @My_IP_set_variable_name.

{
   "RuleVariables":{
      "IPSets":{
         "HTTP_SERVERS":{
            "Definition":[
               "10.0.2.0/24",
               "10.0.1.19"
            ]
         }
      },
      "PortSets":{
         "HTTP_PORTS":{
            "Definition":[
               "80",
               "8080"
            ]
         }
      }
   },
   "ReferenceSets":{
      "IPSetReferences":{
         "BETA":{
            "ReferenceArn":"arn:aws:ec2:us-east-1:555555555555:prefix-list/pl-1111111111111111111_beta"
         }
      }
   },
   "RulesSource":{
      "RulesString":"drop tcp @BETA any -> any any (sid:1;)"
   }
}

Standard stateful rule groups

The following JSON shows an example rule definition for a Network Firewall basic stateful rule group. 

{
    "RulesSource": {
        "StatefulRules": [
          {
            "Action": "DROP",
            "Header": {
                "Protocol": "HTTP",
                "Source": "$HOME_NET",
                "SourcePort": "ANY",
                "Direction": "ANY",
                "Destination": "$EXTERNAL_NET",
                "DestinationPort": "ANY"
            },
            "RuleOptions": [ {
                    "Keyword": "msg",
                    "Settings": [ "\"this is a stateful drop rule\""
                    ]
                },
                {
                    "Keyword": "sid",
                    "Settings": [ "1234"
                    ]
                }
            ]
        }
      ]
    }
}

The following Suricata rules listing shows the rules that Network Firewall generates for the above deny list specification.

drop http $HOME_NET ANY <> $EXTERNAL_NET ANY (msg:this is a stateful drop rule; sid:1234;)