Subdomain takeover is cybersecurity flaw in which an attacker is able to take control of an associated subdomain of the main domain.
This vulnerability could result in numerous security threats, such as redirecting traffic, phishing or any other malicious activity within the subdomain.
This article will dive into the meaning of subdomain takeover. The time it happens, and what you can do to avoid it from happening.
To find out whether a username or username is available, you can use a namechecker or username availability checker.
Key Highlights
- A subdomain takeover happens when a hacker takes advantage of a flaw in the subdomain’s DNS configuration and assumes the domain’s ownership or subdomain.
- The takeover could result in numerous security threats, such as the redirection of traffic, phishing or any other malicious activity within the subdomain. Which highlights the importance of vigilant DNS (Domain Name System) management as well as timely removal of the subdomain.
- Subdomain takeovers can occur in the provisioning and de-provisioning process of web services in particular when DNS records aren’t appropriately controlled or when services are not in use anymore.
- Subdomain takeovers can be avoided through a variety of practices, such as setting up standard procedures when making provisioning or de-provisioning of resources. Utilizing only reliable web hosting providers, and enlisting ethical hackers, and much more.
Page Contents
What is Subdomain Takeover?
Subdomain takeover occurs when hackers take control of a subdomain which is part of an overall domain.
Subdomains are used for specific purposes, such as hosting services or web applications. If a hacker gains the control of a subdomain they may alter content, redirect traffic or launch attacks. Which could endanger the reputation of the parent domain as well as its security.
If subdomains aren’t properly kept, they’re vulnerable to the security vulnerability. Subdomain takeovers can also happen when a subdomain connects to services from outside. Which are not under the supervision of the domain owner’s parent.
When Do Subdomain Takeover Vulnerabilities Occur?
Subdomain takeover typically occurs when a subdomain is set up in order to link to specific platform or service, like Shopify or GitHub Pages. Heroku and others, however the services or other content that is on the subdomain have been relocated or removed.
This allows hackers to take advantage of this vulnerability and gain access the subdomain. It’s like having a marker in a direction that is no longer there. This creates a security hole that can be exploited.
How Are Subdomain Takeovers and DNS Records Related?
DNS (Domain Name System) records are the configurations that link human-readable domain names to their respective IP addresses or provide important information regarding domains as well as email service. There are various kinds of DNS records like “A” records “AAA” records CNAME records and many more.
The subdomain takesover and DNS records are linked because the subdomain takes over usually happens. Because of the existence of a CNAME record that identifies an address that is no longer in use or deleted. Inflicted by malicious parties, they can exploit this weakness and assert control over an previously valid subdomain.
How Does Subdomain Takeover Happen?
Subdomain takeovers can occur during the process of deprovisioning or provisioning.
This is how it happens in both situations.
- During Provisioning
Subdomain takeovers during the provisioning process is extremely uncommon, but it can happen in some situations. It usually happens when an attacker is able to influence or alter the initial configuration of a subdomain to achieve purposeful reasons.
Imagine you own a site for your business online and you’d like to establish a blog subdomain section on your site.
You’ll need to establish the blog.website.com subdomain.
In order to set up a subdomain for your primary domain. You must create DNS records to redirect users on a journey to get them onto your website.
In the end, you must establish a virtual hosting account with your hosting provider to allow users have access to the subdomain.
If you don’t set up an online host within the timeframe or your hosting service does not verify. That the person who is requesting this virtual hosting account is actually the person who owns the domain. Hackers could exploit this vulnerability and carry out an attempt to take over the subdomain.
- During Deprovisioning
Subdomain takeovers during deprovisioning generally occurs. When the owners of websites take away the virtual host, but they don’t take out their DNS record that identifies the host virtual. This allows hackers to take advantage of this affected DNS record to set up their own virtual hosts on your behalf.
This would allow the hacker to host harmful content on your subdomain that you control.
For instance, if don’t would like hosting an online shop or blog on your website. And take down your virtual hosting provider, you’ll have to remove the DNS records to ensure subdomain takeover doesn’t happen in the process of deprovisioning.
The Dangers of Subdomain Takeover How Can Hackers Work Using Subdomains?
Subdomain takeover can pose a number of dangers for your site and the content it contains. We have listed them below.
The loss of control over the subdomain’s content. If hackers take control of your subdomain, they will be able to modify its content at any time. They could insert malicious scripts and alter the content of your website or alter content using hazardous content. If you run an internet-based business, it may cause reputational damage.
Attackers are able to exploit subdomain takeovers. In order to steal cookies of visitors that are connected to a compromised website. Cookies can contain sensitive information regarding visitors, including passwords for logins. Session tokens as well as other personal information which can be used to gain access.
Subdomain takeovers offer an ideal platform to start phishing campaigns. Hackers could use your domain to make fake websites that look like legitimate ones that are hosted on compromised subdomains. Making users provide confidential data.
DDoS attacks – The compromised subdomain could be used to start distributed denial of service (DDoS) DDoS attacks.
Subdomain takeover is another attack that could enable hackers to distribute other malware. Or carry out other attacks, such as XSS, CSRF, CORS bypass, and much more.
Subdomain Takeover Examples
Let’s look at the most popular subdomain takeovers that are found on reliable websites and other services. Read on to find out more.
Subdomain Takeover GitHub
Subdomain takeovers via GitHub is possible in the following circumstances:
The hacker finds that certain resources that are hosted on GitHub pages are no longer being used
However, they still have DNS configurations for the subdomain vulnerable to attack that connects to them.
Let’s say there’s an entity that runs the website “mywebsite.com” and also has an GitHub Pages website hosted at “username.github.io” to promote their own project.
If the company decides it no longer requires the GitHub repository that is associated with this domain. However, it then forgets to remove it from the DNS record for the subdomain.
Today, hackers are able to use the subdomains to host malicious code as well as other web pages to trick or even exploit the users.
Azure Subdomain Takeover
Microsoft Azure is among the most well-known and reputable cloud providers, so that vulnerabilities aren’t difficult to find. Similar to other cloud providers, Microsoft Azure uses one-to-one mapping to its cloud services as well as virtual machines.
When making an DNS record Microsoft Azure performs ownership verification by using TXT records to verify “A” DNS entries. But, this doesn’t apply to the CNAME record, which allows for subdomain takeover risk.
Let’s say you created an Azure resource that had an Fully qualified Domain Name (FQDN) however, after you no longer required it, you either deprovisioned or deleted the resource. You didn’t delete your CNAME records from the DNS zone. This caused the domain name that is canonical being recognized as a valid domain.
If a shady party such as hacker is able to discover the hanging subdomain, they’ll create the new Azure resource using the same FQDN as the resource you removed. The resource can then redirect users to the hackers server which hosts malware and other files.
Subdomain Takeover with an expired Domain
A subdomain takeover could happen if you own an expired domain and you did not renew it.
Let’s suppose that you own your website “example.com” and you decided to establish a subdomain “blog.example.com” in order to host blog posts on your website. The subdomain utilizes an CNAME record to provide a link to the main domain.
After a while the domain was defunct, but the CNAME record didn’t disappear out of the example.com DNS zone, which means it was vulnerable to CNAME domain takeovers.
A hacker chooses to register blog.example.com and uses the domain to store malicious information, causing confusion to visitors and even swindling them.
How to Prevent Subdomain Takeover?
It is vital to prevent subdomain takeover since it protects your web image and reputation. If subdomains become vulnerable, attackers could use their vulnerability to deceive users, steal confidential data, or host harmful content.
To reduce the danger, you must be proactive in preventing subdomain acquisitions.
- Set up standard procedures when it comes to providing and deprovisioning hosts: During the process of provisioning, start by claiming the virtual host then, start creating CNAME record or any other DNS entry. If you are deprovisioning, delete DNS records first before you take down from the host.
- Select hosting companies that ensure that anyone who attempts to claim that the virtual host’s domain and subdomain is actually the owner of the domain and subdomain
- Avoid wildcard subdomains by not using wildcard DNS entries, or unintentional URL redirects because they could inadvertently lead to subdomain takeovers.
Find ethical hackers to hack: You might consider the running of bug bounty programs, or enlisting security experts to identify and assess the potential vulnerabilities of subdomain takeovers prior to hackers can exploit them.
Utilize an inventory or asset management software This will help you keep a complete and organized inventory of any digital asset.
Best Subdomain Takeover Tools and Scanners
Subdomain takeover scanners and tools are programs or scripts that are employed by cybersecurity experts and ethical hackers to detect weaknesses in subdomains of a domain. This is a list the top subdomain takeover tools and scanners.
Subjack written using Go language, hackers who are ethical are able to utilize Subjack to scan concurrently subdomains to hunt for bugs.
- Tko-subs: It’s another tool that utilizes Go and helps to identify subdomains that are dangling. It will help you find points to CMS providers. And also detect links that lead to hostnames which are no more in use or have been deleted. It also assists in the case of DS records that contain typos.
- Tenable: Tenable is a dependable analysis and vulnerability detection tool. That is commonly employed by ethical hackers looking to identify weaknesses in networks of computers. It assists in identifying hanging DNS records as well as other issues that could lead to subdomain takeover.
- DNSTake: DNSTake is another tool that is able to quickly identify hanging DNS records. And also check for the absence of DNS zones to guard against vulnerabilities of various kinds.
Conclusion
Subdomain takeover poses a significant security risk that could become a target for malicious hackers to break into web-based applications.
To stop it from happening, organizations must:
- Monitor and regularly manage the DNS records of your DNS
- Remove subdomains that are not being used.
- Use proper access control.
The importance of proactive and vigilant measures is crucial to reducing this risk and securing online assets.
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