how to check for subdomain takeover

Guri Bee

3 min read

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16-10-2024

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Unmasking the Subdomain Takeover Threat: A Practical Guide for Security Professionals

Subdomain takeover is a common web security vulnerability that allows attackers to gain control of a subdomain, potentially hijacking traffic and compromising sensitive data. This article will guide you through the process of identifying and mitigating this threat, using real-world examples and practical advice.

What is Subdomain Takeover?

Imagine a company owns the domain "example.com" and uses a subdomain "blog.example.com" to host their blog. If the company decides to discontinue the blog, they might delete the associated DNS record for "blog.example.com". However, if the company didn't configure the subdomain to point to a "parking page" or a "not found" page, the subdomain could become vulnerable to takeover.

An attacker could register "blog.example.com" with a web hosting service, essentially claiming ownership of the subdomain. They could then redirect traffic to their malicious website, potentially compromising users' sensitive information or spreading malware.

How to Identify Subdomain Takeovers

Here are some strategies to identify potential subdomain takeovers:

1. Utilize Subdomain Enumeration Tools:

• Example: Sublist3r (Author: TheRook)

  "Sublist3r is a Python tool designed to enumerate subdomains of a given domain. It uses various search engines and APIs to extract subdomains."

  • GitHub Repository

  Sublist3r can be used to generate a list of subdomains, allowing you to identify potentially vulnerable subdomains.

• Example: Amass (Author: OWASP Amass Project)

  "Amass is a powerful, open-source tool designed to enumerate subdomains and perform passive DNS reconnaissance."

  • GitHub Repository

  Amass uses various techniques, including passive DNS, internet-wide crawling, and web scraping, to discover subdomains. It can also generate reports and graphs to visualize the collected data.

2. Analyze DNS Records:

• Example: DNSdumpster (Author: Open Source)

  "DNSdumpster is a free online tool that provides DNS and WHOIS information about a domain. It helps you identify potential vulnerabilities by analyzing DNS records and looking for misconfigured subdomains."

  • Website

  By analyzing DNS records, you can identify subdomains that point to non-existent or inactive web servers, making them potential targets for takeover.

3. Utilize Security Scanning Services:

• Example: Burp Suite (Author: Portswigger)

  "Burp Suite is a professional security testing tool that includes a wide range of features, including a powerful subdomain takeover scanner. It can automate the process of identifying vulnerable subdomains and provide detailed reports."

  • Website

  Specialized scanning services like Burp Suite can automate the process of identifying potential subdomain takeovers by analyzing DNS records and web server configurations.

Mitigation Strategies

1. Implement DNS Parking or Redirection:

• Configure subdomains to point to a dedicated "parking page" or a "not found" page when they are not in use.
• This prevents attackers from registering the subdomain and redirecting traffic to their own servers.

2. Regularly Review and Clean Up DNS Records:

• Regularly audit DNS records for inactive subdomains.
• If a subdomain is no longer in use, delete the associated DNS record promptly.

3. Implement Security Best Practices:

• Strong Password Policies: Ensure that all accounts associated with subdomains use strong passwords and are protected with multi-factor authentication.
• Secure Server Configuration: Configure web servers with the latest security patches and minimize potential attack surfaces.
• Monitoring and Alerting: Use monitoring tools to detect suspicious activity related to your subdomains and receive alerts in real-time.

Additional Considerations:

• Cloud Services: If your subdomain is hosted on a cloud platform, be aware of the specific security measures and best practices recommended by the provider.
• Third-party Services: If you use third-party services that manage your subdomains, ensure they have robust security measures in place to prevent takeover attempts.

Conclusion:

Subdomain takeover is a serious security threat that can lead to data breaches, website hijacking, and reputational damage. By using the techniques outlined in this article, you can proactively identify and mitigate this vulnerability, protecting your organization's digital assets. Remember, regular security audits, proactive monitoring, and timely response to potential threats are crucial for ensuring the safety of your online presence.