onaws is a simple tool to check if an IP/hostname belongs to the AWS IP space or not. It uses the AWS IP address ranges data published by AWS to perform the search.

The tool could be helpful in:

• Continuous recon of assets
• Gathering assets that use a specific service (e.g. EC2)
• Subdomain/DNS takeovers
• Finding region information for S3 buckets
• etc.

pip install onaws

pip install -U onaws

onaws 52.219.47.34

A domain or subdomain can be passed as input:

onaws example.com

You may also supply an S3 bucket hostname as input:

onaws dropbox.s3.amazonaws.com

onaws accepts line-delimited hosts on STDIN. This is helpful if you want to pipe the output of other tools to onaws:

$ cat hosts.txt
uber.s3.amazonaws.com
aws.com
google.com
23.21.52.140


$ cat hosts.txt | onaws
{
    "is_aws_ip": true,
    "ip_address": "52.218.106.162",
    "service": "S3",
    "region": "eu-west-1",
    "matched_subnet": "52.218.0.0/17",
    "hostname": "uber.s3.amazonaws.com"
}
{
    "is_aws_ip": true,
    "ip_address": "143.204.225.9",
    "service": "CLOUDFRONT",
    "region": "GLOBAL",
    "matched_subnet": "143.204.0.0/16",
    "hostname": "aws.com"
}
{
    "is_aws_ip": false,
    "ip_address": "216.58.201.238",
    "hostname": "google.com"
}
{
    "is_aws_ip": true,
    "ip_address": "23.21.52.140",
    "service": "EC2",
    "region": "us-east-1",
    "matched_subnet": "23.20.0.0/14"
}

onaws accepts hostnames as input, but it resolves them individually with no optimization. Therefore, it's significantly faster to do the resolution first with a tool like MassDNS or dnsx:

cat hosts.txt | dnsx -silent -a -resp-only | onaws

If the IP/hostname falls in the AWS IP range, onaws will return the service, region and other details in the output:

{
    "is_aws_ip": true,
    "ip_address": "52.218.196.155",
    "service": "S3",
    "region": "us-west-2",
    "matched_subnet": "52.218.128.0/17",
    "hostname": "flaws.cloud"
}

For multiple inputs, the output format will be in JSONL:

{
    "is_aws_ip": true,
    "ip_address": "143.204.225.9",
    "service": "CLOUDFRONT",
    "region": "GLOBAL",
    "matched_subnet": "143.204.0.0/16",
    "hostname": "aws.com"
}
{
    "is_aws_ip": false,
    "ip_address": "216.58.201.238",
    "hostname": "google.com"
}
{
    "is_aws_ip": true,
    "ip_address": "23.21.52.140",
    "service": "EC2",
    "region": "us-east-1",
    "matched_subnet": "23.20.0.0/14"
}

If you want to save the output to a file, you can use Bash redirection or tee:

cat hosts | onaws | tee -a output.json

To get hosts that use EC2:

cat output.json | jq -scr '.[] | select(.service == "EC2") | .hostname'

Output:

groove.uber.com
photos.uber.com
photography.uber.com
...

To get a list of hosts that use AWS services:

cat output.json | jq -sc '.[] | select(.is_aws_ip == true ) | [.hostname, .ip_address, .service] | join (",")' 

Output:

assets-share.uber.com,52.84.13.77,CLOUDFRONT
groove.uber.com,3.223.41.171,EC2
devbuilds.uber.com,52.84.13.29,CLOUDFRONT
photos.uber.com,54.237.133.81,EC2
...

If the input you provide is an invalid IP or is not resolvable, the output will indicate so:

$ onaws 'invalid.invalid'
{
    "hostname": "invalid.invalid",
    "resolvable": false
}

If, for some reason, the tool fails to fetch the AWS IP ranges, it will throw the following exception:

$ onaws
Failed to get AWS IP ranges

I welcome contributions from the public. If you find something that could be improved, please file an Issue or send a PR :)

• Thanks to @TomNomNom for suggesting the name.