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Subdomain takeover from scratch to advance

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Sub-domain Takeover : 

Sub-domain takeover is a common and most popular vulnerability. If you are not aware of such kind of vulnerability, you can understand it as a class of security issues where the intention of an attacker is to take control of an organization’s sub-domain via cloud services.

Sub-domain takeover vulnerability sometimes may lead to financial loss of an organization and compromising users trust on the organization because, this vulnerability attacker can fully claim the particular sub-domain of an organization, on which people have their fail as the secure domain. In some dangerous cases, the attacker exploits the sub-domain takeover vulnerability and puts forms on the sub-domain that is vulnerable and steals confidential information from the user. This information may contain credit/debit card details, CVV or any other personal and confidential information of a user. 

Cause of sub-domain takeover Vulnerability :

Sub-domain takeover arises when a sub-domain is pointing to another domain(CNAME) that doesn’t exist currently. If an attacker registers the non-existing domain, then the sub-domain points to the domain registration by the attacker. A single change in DNS makes the attacker as an owner of that particular sub-domain and he can manage the sub-domain according to his choice. So, this is the power of “sub-domain Takeover Vulnerability”.

Impact :  

It gives an opportunity to the attacker to use a sub-domain on behalf of the organization for any malicious purpose.

Example :

You can consider an example where let’s say, “example” is an organization and the domain is You can also see in the diagram that,, and are the sub-domain’s. Let’s have a look at the diagram to understand sub-domain takeover.

Sub-domain Takeover

Diagram sub-domain takeover explanation –

If is the main domain (high-level domain) of an organization and developers of create a sub-domain , but there is no host which provides content for it, then an attacker can provide a host for this sub-domain (ex. and take the ownership of sub-domain. This leads to sub-domain takeover vulnerability.

Mitigation :

  1. Monitor your digital infrastructure of the website on a regular basis.
  2. Delete the DNS configuration of the external service on your sub-domain if it’s pointing to a non-existing service or host.
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Last Updated : 16 Jun, 2022
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