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Subdomain takeover from scratch to advance

  • Last Updated : 16 Feb, 2021

Sub-domain Takeover : 

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

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Sub-domain takeover vulnerability sometimes may lead to financial loss organization, compromise of users trust on the organization because in this vulnerability attacker can completely 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 put the forms on the sub-domain that is vulnerable and take the confidential information from the user this information may contain credit/debit card detail, 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 not exist currently. If an attacker registers that non-existing domain then the sub-domain points to the domain registration by the attacker. By a single change in DNS make the attacker as an owner of that particular sub-domain and after that attacker can manage the sub-domain according to his choice and 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 the example is an organization and the domain is an example.com and as you can clearly see in the diagram blog.example.com, ads.example.com, and info.example.com are sub-domain. Let’s have a look to understand sub-domain takeover.

Sub-domain Takeover

Diagram sub-domain takeover explanation –

If http://example.com/ is the main domain (high-level domain) of organization and developers of http://example.com/ create a sub-domain http://blog.example.com/ but there is no host which providing content for it then an attacker can provide a host for this sub-domain (ex.http://blog.example.com/) and take the ownership of sub-domain and this leads to sub-domain takeover vulnerability.

Mitigation :

  1. Monitor your digital infrastructure of the website on 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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