Subdomain Takeover

Subdomain Takeover is a malicious activity that the victim’s subdomain allows attackers to control and impersonate.

Automation

• dnsReaper

  git clone https://github.com/punk-security/dnsReaper.git
  cd dnsReaper
  python3 -m venv venv
  source venv/bin/activate
  pip3 install -r requirements.txt
  
  # Fetching from AWS
  python3 main.py aws --aws-access-key-id AWS_ACCESS_KEY_ID --domain example.com
  # Fetching from Azure
  python3 main.py azure --az-subscription-id AZ_SUBSCRIPTION_ID --domain example.com
  # Reading BIND zone file
  python3 main.py bind --bind-zone-file /path/to/zone/file --domain example.com
  # Fetching from Cloudflare
  python3 main.py cloudflare --cloudflare-token CLOUDFLARE_TOKEN --domain example.com
  # Fetching from DigitalOcean
  python3 main.py digitalocean --do-api-key DO_API_KEY --domain example.com
  # Reading specific file
  python3 main.py file --filename /path/to/file --domain example.com
  # Scanning a single domain
  python3 main.py singla --domain example.com --domain example.com

Testing - A, CNAME Subdomain Takeover

1. Enumerate Subdomains

There are various ways to enumerate subdomains.

subfinder -d example.com

# https://github.com/darkoperator/dnsrecon
./dnsrecon.py -d example.com

Please refer to Subdomain Discovery to check more details.

2. Identify Misconfigurations for Subdomains

Check DNS records for identifying what’s on the destination of the subdomain.

dig A app.example.com
dig CNAME app.example.com

Also we can try to access them with web browser or command-line. For example,

# -L: Follow redirect
# -v: Verbose mode
curl -Lv app.example.com
curl -v cloud.example.com
curl -v mail.example.com

3. Spoof with the Subdomain

If a certain subdomain can be accessible but the error page of the specific provider (e.g. GitHub, Google Cloud, Wix, etc.) appeared, it means that the subdomain of the settings in the service provider was removed but the DNS record (e.g. A, CNAME) remains yet.

In short, attackers can spoof as a legitimate site by claiming this subdomain in the provider.

Here’s an abstract example:

1. Login the target provider.

2. Create a malicious website.

3. Add the target subdomain (e.g. app.example.com) as custom domain in the setting page.

4. If users visit app.example.com, they have now visited a malicious website created by an attacker.

Testing - NS Subdomain Takeover

It’s more dangerous If NS record is vulnerable because if the nameserver is taken over, an attacker can take full control of victim’s domains.

To gather NS records for the target domain, use dig command.

dig ns example.com +short

# Result examples
ns-100.abcde.org
ns-120.abcde.co.uk

Next, check if the gathered domains can be purchased with domain name registrar like GoDaddy, NameCheap.

For example, search [abcde.org](http://abcde.org) in the domain search page of NameCheap. If this domain can be purchased, attackers can buy this domain then take control the name resolution of a victim by creating the custom nameserver which pointed to this domain.