Subjack is a Subdomain Takeover tool written in Go designed to scan a list of subdomains concurrently and identify ones that are able to be hijacked. With Go's speed and efficiency, this tool really stands out when it comes to mass-testing. Always double check the results manually to rule out false positives.

Subjack will also check for subdomains attached to domains that don't exist (NXDOMAIN) and are available to be registered. No need for dig ever again! This is still cross-compatible too.

Subdomain takeover vulnerabilities occur when a subdomain ( is pointing to a service (e.g. GitHub pages, Heroku, etc.) that has been removed or deleted. This allows an attacker to set up a page on the service that was being used and point their page to that subdomain. For example, if was pointing to a GitHub page and the user decided to delete their GitHub page, an attacker can now create a GitHub page, add a CNAME file containing, and claim

There are several tools with dictionaries to check for possible takeovers:

Subdomain Takeover Generation via DNS Wildcard

When DNS wildcard is used in a domain, any requested subdomain of that domain that doesn't have a different address explicitly will be resolved to the same information. This could be an A ip address, a CNAME...

  • For example, if * is wilcarded to Then, will be pointing to

However, if instead of pointing to an IP address, the sysadmin point it to a third party service via CNAME, like a github subdomain for example ( An attacker could create his own third party page (in Gihub in this case) and say that is pointing there. Because, the CNAME wildcard will agree the attacker will be able to generate arbitrary subdomains for the domain of the victim pointing to his pages.

Exploiting a subdomain takeover

Subdomain takeover is essentially DNS spoofing for a specific domain across the internet, allowing attackers to set A records for a domain, leading browsers to display content from the attacker's server. This transparency in browsers makes domains prone to phishing. Attackers may employ typosquatting or Doppelganger domains for this purpose. Especially vulnerable are domains where the URL in a phishing email appears legitimate, deceiving users and evading spam filters due to the domain's inherent trust.

SSL Certificates

SSL certificates, if generated by attackers via services like Let's Encrypt, add to the legitimacy of these fake domains, making phishing attacks more convincing.

Cookie Security and Browser Transparency

Browser transparency also extends to cookie security, governed by policies like the Same-origin policy. Cookies, often used to manage sessions and store login tokens, can be exploited through subdomain takeover. Attackers can gather session cookies simply by directing users to a compromised subdomain, endangering user data and privacy.

Emails and Subdomain Takeover

Another aspect of subdomain takeover involves email services. Attackers can manipulate MX records to receive or send emails from a legitimate subdomain, enhancing the efficacy of phishing attacks.

Higher Order Risks

Further risks include NS record takeover. If an attacker gains control over one NS record of a domain, they can potentially direct a portion of traffic to a server under their control. This risk is amplified if the attacker sets a high TTL (Time to Live) for DNS records, prolonging the duration of the attack.


1. Install subjack

  • go install

2. Display help menu

  • subjack -h

How to use

1. Find the fingerprints.json file

  • find -type f -name "fingerprints.json"

2. Run this tool against a subdomain list

  • subjack -w subdomains.txt -t 100 -timeout 30 -o results.txt -ssl -c ./go/pkg/mod/ -v 3

3. Save the output to a file

  • subjack -w ./Desktop/URL-list.txt -t 100 -timeout 30 -o results.txt -ssl -c ./go/pkg/mod/ -v 3 -o results.txt

4. Search by single domain,or sub-domain

  • subjack -d -t 100 -timeout 30 -o results.txt -ssl -c ./go/pkg/mod/ -v 3


  • -d if you want to test a single domain.
  • -w domains.txt is your list of subdomains.
  • -t is the number of threads (Default: 10 threads).
  • -timeout is the seconds to wait before timeout connection (Default: 10 seconds).
  • -o results.txt where to save results to. For JSON: -o results.json
  • -ssl enforces HTTPS requests which may return a different set of results and increase accuracy.
  • -a skips CNAME check and sends requests to every URL. (Recommended)
  • -m flag the presence of a dead record, but valid CNAME entry.
  • -v verbose. Display more information per each request.
  • -c Path to configuration file.


  • Removing vulnerable DNS records - This is effective if the subdomain is no longer required.
  • Claiming the domain name - Registering the resource with the respective cloud provider or repurchasing an expired domain.
  • Regular monitoring for vulnerabilities - Tools like aquatone can help identify susceptible domains. Organizations should also revise their infrastructure management processes, ensuring that DNS record creation is the final step in resource creation and the first step in resource destruction.