Subdomain Takeover Attack

April 25, 2023 / By Securium Solutions

What is Subdomain:-

A subdomain is a domain that is a part of a larger domain name. It is used to organize and categorize content on a website, or to create separate sections of a website for different purposes. For example, the subdomain “blog” in the domain name “” indicates that the website contains a blog section. Subdomains are created by adding a prefix to the main domain name and separating it with a dot. For example, the subdomain “shop” can be added to the main domain name “” to create the subdomain “” or Subdomain takeover. Subdomains can be used to host different types of content, such as blogs, forums, or e-commerce stores, and can be assigned different IP addresses or servers.

What is Subdomain Takeover:-

Subdomain takeover occurs when a subdomain of a website points to an inactive or unused resource that an attacker can take control of. This can happen when a website owner forgets to remove a subdomain that was previously used for a third-party service (subdomain takeover aws), or when the service provider removes the account associated with the subdomain. When this happens, the subdomain may still be pointing to the now-defunct resource, leaving it vulnerable to takeover by an attacker.

Here are the steps an attacker may take to perform a Subdomain takeover:-

1. Identify potential target subdomains – This can be done by searching for publicly available DNS records, using subdomain enumeration tools, or by manually checking for subdomains associated with a specific service or application.

2.  Check if the subdomain is vulnerable – An attacker may attempt to access the subdomain and check if it’s still pointing to a service or application that is no longer in use. They may also try to brute-force the subdomain’s DNS records to identify any possible vulnerabilities.

3. Register the service or application – If the subdomain is vulnerable, an attacker may register the service or application that was previously associated with it. This can be done by creating an account with the service provider or by deploying a dummy application on the subdomain.

4. Take control of the subdomain – Once the attacker has registered the service or application, they can update the DNS records for the subdomain to point to their own servers. This allows them to take control of the subdomain and potentially access sensitive information or carry out other attacks

The most common scenario of this process follows:

1. The domain name (e.g., uses a CNAME record to another domain (e.g., CNAME

2. eventually runs out of time and becomes open for registration by anyone.

3. Since the CNAME record is not deleted from the DNS zone, anyone who registers has full control over until the DNS record is present.

Risks of Subdomain Takeover:-

Subdomain takeover can pose serious risks to website owners, including:

1. Malware Distribution: Attackers can use a subdomain to host malware, which can be distributed to website visitors.

2. Phishing Attacks: Attackers can use a subdomain to host phishing pages that mimic legitimate websites and steal sensitive information from visitors.

3. Blacklisting: If a subdomain is used to host malicious content, the entire domain may be blacklisted by search engines and other security providers, affecting the website’s reputation and traffic.

How to avoid subdomain Takeover:-

1. Regularly review your DNS settings: Regularly review your DNS settings to ensure that all subdomains are pointing to active and secure resources.

2. Remove unused subdomains: If a subdomain is no longer in use, remove it or point it to a safe landing page.

3. Monitor subdomains: Use subdomain monitoring tools to receive alerts when subdomains are added or removed from your DNS settings, allowing you to detect potential takeover attempts early.

4. Stay informed: Stay up-to-date with the latest subdomain takeover techniques and vulnerabilities, and implement best practices to prevent them.


Subdomain takeover is a serious security risk that can leave your website vulnerable to attacks. By understanding how Fastly Subdomain takeover happens and implementing best practices to prevent it, you can protect your website from potential threats and ensure the security of your users’ data. Remember to regularly review your DNS settings, remove unused subdomains, monitor subdomains, and stay informed about the latest vulnerabilities and techniques used by attackers.


Lokesh Yadav

(Cyber Security Intern)

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