What is Subdomain Hijacking? Learn How to Prevent It

by | Nov 23, 2024 | Web development

Subdomain hijacking is a growing information technology security or electronic information security threat that many businesses face today. It can harm your website, reputation, and users. This article will explain subdomain hijacking, how it works, and, most importantly, how you can stop it from happening.

What is Subdomain Hijacking?

A subdomain is a smaller part of your main website. For example, if your website is example.com, a subdomain could be blog.example.com or store.example.com.

Subdomain hijacking happens when hackers take over a subdomain that has been left vulnerable. This usually occurs when a subdomain is linked to a third-party service (like a hosting provider or a cloud storage platform) that you’re no longer using, but the subdomain still exists in your DNS records.

Why is This a Problem?

When attackers hijack your subdomain, they can:

  • Host malicious content under your name.
  • Use it for phishing attacks to steal sensitive data.
  • Harm your business reputation.

How Does Subdomain Hijacking Work?

Here’s a simple breakdown of how subdomain hijacking happens:

  1. Unused Subdomains
  2. You set up a subdomain to link to a service, such as AWS, Heroku, or GitHub Pages. Later, you stop using that service but forget to remove the subdomain’s DNS record.
  3. Attackers Identify Weakness
  4. Hackers scan the internet for these inactive subdomains with DNS records still pointing to services that no longer exist.
  5. Exploitation
  6. The attacker registers the resource (like a cloud bucket or a page) and links it to your subdomain. Now, they control what’s displayed on that subdomain.

Real-Life Examples

Microsoft’s Subdomain Hijacking Incident (2019)

In 2019, Microsoft faced subdomain hijacking on mybrowser.microsoft.com. Hackers used this subdomain to host phishing content, damaging the company’s reputation.

Indian E-commerce Sites (2023)

Recent reports in 2023 revealed that over 15% of subdomains of popular Indian e-commerce sites were vulnerable to hijacking. Cybersecurity firm CloudSEK identified these issues and warned companies to fix them quickly.

Statistics

  • A study by Rapid7 in 2022 found that 25% of websites with third-party integrations have at least one misconfigured subdomain.
  • Google flagged 1.2 million phishing sites in 2023, some of which used hijacked subdomains.

Why is Subdomain Hijacking Dangerous?

Subdomain hijacking is not just a technical issue—it can have real-world consequences:

  1. Loss of Trust
  2. Customers might see harmful content on your subdomain and lose trust in your brand.
  3. Legal Problems
  4. Hosting illegal or malicious content can lead to lawsuits or regulatory action.
  5. SEO Damage
  6. Search engines like Google may penalize your domain, affecting your website’s ranking.
  7. Data Breaches
  8. Hackers may use your subdomain to trick users into sharing sensitive information.

How to Check if Your Subdomains are Safe

Here are some simple ways to check your subdomains:

  1. Use Online Tools
  2. Tools like Sublist3r, Amass, or Subfinder can scan your domain and list all subdomains.
  3. Check for Misconfigurations
  4. Look for subdomains still pointing to unused services.
  5. Monitor DNS Records
  6. Regularly review your DNS settings to ensure all records are necessary and secure.

How to Prevent Subdomain Hijacking

1. Audit Your Subdomains Regularly

  • Make a list of all your subdomains and their purposes.
  • Remove unused or unnecessary subdomains immediately.

2. Update DNS Records

  • Ensure DNS records are accurate and don’t point to inactive services.
  • Delete records for services you no longer use.

3. Use Third-Party Services Responsibly

  • If you’re using platforms like AWS or GitHub Pages, deactivate the service and update DNS when you’re done using it.

4. Monitor Your Domain

  • Set up alerts for any changes in your domain’s DNS records. Tools like DNS Spy can help.

5. Secure Subdomains with HTTPS

  • Use SSL certificates for all your subdomains. This adds a layer of security.

6. Enable DNSSEC

  • DNSSEC (Domain Name System Security Extensions) ensures that DNS responses are authentic and not tampered with.

7. Educate Your Team

  • Train your employees to manage subdomains securely and follow best practices.

8. Use Vulnerability Scanners

  • Regularly scan your website and subdomains for vulnerabilities using tools like Burp Suite or Acunetix.

What to Do If Your Subdomain is Hijacked

  1. Identify the Problem
  2. Use monitoring tools to find which subdomain has been hijacked.
  3. Remove DNS Records
  4. Log into your domain registrar and delete the DNS record for the hijacked subdomain.
  5. Reclaim the Subdomain
  6. If possible, register the resource (like an AWS bucket) back under your control.
  7. Inform Your Users
  8. Let your customers know about the issue and advise them to avoid the hijacked subdomain.
  9. Report the Incident
  10. Report the malicious activity to your hosting provider or the platform being misused.

Why Prevention is Better Than Cure

Fixing a hijacked subdomain can take days or weeks, during which your website’s reputation and user trust may suffer. Prevention is easier, cheaper, and more effective.

Real-Time Tools to Help You

  1. Cloudflare
  2. Protect your domain and subdomains with Cloudflare’s DNS security features.
  3. Google Search Console
  4. Monitor your domain and subdomains for issues.
  5. Sucuri
  6. A robust website firewall and monitoring service to detect vulnerabilities.

Conclusion

Subdomain hijacking is a serious threat, but it’s preventable. By auditing your DNS records, monitoring subdomains, and following security best practices, you can protect your website and your users.

Don’t wait for an attack to happen. Take action today to secure your online presence and ensure your customers’ trust.

Ashish Tiwari
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