Dangling ‐ Stale CNAME DNS record exploited by threat actor - ToddMaxey/Technical-Documentation GitHub Wiki

Customer has discovered that an attacker exploited a dangling or stale CNAME DNS record associated with their domain. Although they have cleaned up the CNAME record and related Azure resources, they discovered that a DigiCert certificate is still being issued through Microsoft. This indicates that the attacker may still have the ability to impersonate the domain or intercept traffic intended for it.

Layperson explanation: What Happened and Why It Matters:

Think of your website’s addresses (DNS records) like directions for visitors finding your business online. If one of those directions, known as a CNAME record, pointed to a location that used to belong to you but no longer does, it can be taken over by someone else—an attacker. This is like forgetting to remove a sign that sends customers to a building you no longer rent, where someone else can now pretend to be you. This type of oversight allowed an attacker to set up a fake service at the old “address.” Worse yet, they managed to obtain a security certificate—a piece of digital proof that usually verifies a site’s identity. With this certificate, they can pose as your organization to trick visitors or intercept information intended for you.

Course of Action to Address this Issue:

  1. Report the Issue to Microsoft Security Response Center (MSRC):

    Why: Since the issue involves Azure resources and certificates issued through Microsoft, it's essential to notify Microsoft so they can investigate and take appropriate action.

    How to Report:

    Submit a Vulnerability Report:

    • Visit the Microsoft Security Response Center (MSRC) Submission Portal.
    • Provide a detailed report including:
    • A summary of the issue.
    • Steps to reproduce the problem (if possible).
    • The specific CNAME record and any associated Azure resources.
    • Details about the unauthorized DigiCert certificate issuance.
    • Any logs or evidence of the attacker's activity.
    • Contact information for follow-up.

    Urgent Assistance:

    If you believe this issue requires immediate attention, you can contact MSRC via email at [email protected].

    Reference:

    MSRC Reporting Guidelines

  2. Notify DigiCert of Unauthorized Certificate Issuance:

    • Why: As the Certificate Authority (CA), DigiCert can revoke the unauthorized certificate to prevent misuse.

    • How to Report:

    • Contact DigiCert Support:

    • Provide:

      • Proof of domain ownership.
      • Details of the unauthorized certificate, including the certificate's serial number and issuance date.
      • Explanation of the situation and steps already taken.
      • Request immediate revocation of the certificate.

    • Reference:

  3. Monitor for Other Unauthorized Certificates:

  4. Audit and Secure Your DNS and Cloud Resources:

    • DNS Records:

      • Perform a comprehensive audit of all DNS records.
      • Remove any other stale or unused records.
      • Implement DNS change monitoring to receive alerts on any modifications.

    • Azure Resources:

      • Ensure all Azure resources are properly secured or decommissioned.
      • Review access controls and permissions.
      • Enable logging and monitoring for all services.

  5. Implement DNS Security Measures:

    • DNSSEC:

      • Consider implementing DNS Security Extensions (DNSSEC) to protect against DNS spoofing and cache poisoning.

    • CNAME Flattening:

      • Use CNAME flattening or ALIAS records where appropriate to reduce reliance on external CNAME records.

    1. Internal Incident Response:

      • Root Cause Analysis:

        • Investigate how the dangling CNAME record was left active.
        • Identify any gaps in your decommissioning or change management processes.

      • Update Policies and Procedures:

        • Revise internal guidelines to include periodic reviews of DNS records and cloud resources.
        • Implement stricter controls around DNS changes and resource decommissioning.

      • Staff Training:

        • Educate your IT and security teams about the risks of dangling DNS records.
        • Promote awareness of best practices in DNS and cloud resource management.

    1. Legal and Compliance Considerations:

      • Consult Legal Counsel:

        • Determine if there are any legal obligations to report the compromise to regulatory bodies or affected parties.

      • Data Protection Authorities:

        • If personal data may have been compromised, consider notifying relevant data protection authorities in accordance with laws like GDPR or CCPA.

    1. Inform Stakeholders:

      • Internal Communication:

        • Notify senior management and relevant departments about the incident and steps being taken.

      • External Communication:

        • If there's a risk to customers or partners, prepare a communication plan to inform them transparently.

    1. Enhance Security Monitoring:

      • Set Up Alerts:

        • Configure alerts for any unusual activities related to your domain, such as unexpected certificate issuance or DNS changes.

      • Security Information and Event Management (SIEM):

        • Use a SIEM solution to aggregate and analyze logs from different sources for better threat detection.

    1. Prevent Future Occurrences:

      • Implement Automation:

        • Use automation tools to manage DNS records and cloud resources, reducing the risk of human error.

      • Regular Audits:

        • Schedule periodic security audits to identify and remediate potential vulnerabilities proactively.

      • Access Control:

        • Review and restrict permissions to modify DNS settings and cloud resources to essential personnel only.

Additional Recommendations:

  • Enable Multi-Factor Authentication (MFA):

    • Ensure all accounts, especially those with administrative privileges over DNS and cloud resources, have MFA enabled.

  • Use Conditional Access Policies:

    • Implement policies that restrict access based on factors like location, device compliance, and user risk.

  • Implement Certificate Pinning (if applicable):

  • For critical applications, use certificate pinning to trust only specific certificates.

Promptly reporting the issue to both Microsoft and DigiCert is crucial to mitigate the immediate risk posed by the unauthorized certificate and potential domain impersonation. By taking these steps, you not only address the current security concern but also strengthen your organization's security posture to prevent similar incidents in the future.

References: