One of the biggest challenge of working as SRE is to manage Dangling DNS. These are DNS records that point to resources (like IP addresses, cloud services, or servers) that no longer exist. When not properly managed, dangling DNS records can lead to significant security risks. Let’s delve into what dangling DNS is, the risks associated with it, and how to mitigate these risks effectively.
What is Dangling DNS?
Dangling DNS records occur when DNS entries point to resources that have been decommissioned or are no longer in use. For example, a DNS record might point to an IP address that once hosted a web application but has since been repurposed or released. The DNS record, however, remains, pointing to an address that might be reassigned to another user or service.
Risks Associated with Dangling DNS
Subdomain Takeover: One of the most severe risks is subdomain takeover. If a DNS record points to a decommissioned resource, an attacker can potentially claim the resource and host malicious content at the subdomain.
Phishing and Spoofing: Attackers can exploit dangling DNS records to create convincing phishing pages, spoof legitimate services, or spread malware.
Data Exposure: Misconfigured DNS records can inadvertently expose sensitive data or internal services to the public internet.
Reputation Damage: If an attacker takes over a subdomain, they can use it for malicious activities, which can harm the reputation of the original domain owner.
How to Mitigate Dangling DNS Risks
Regular Audits:
Conduct regular audits of your DNS records to identify and remove any that are no longer associated with active resources.
Implement automated tools to scan for and alert on dangling DNS records.
Strict Decommissioning Procedures:
Ensure that DNS records are updated or deleted as part of the resource decommissioning process.
Create a checklist for decommissioning resources that includes DNS cleanup.
Monitoring and Alerts:
Use monitoring tools to track changes in DNS records and alert administrators to potential issues.
Set up alerts for unusual DNS activity or configuration changes.
Resource Verification:
Regularly verify that DNS records are pointing to active and intended resources.
Implement policies to periodically review and confirm the validity of DNS entries.
Access Controls:
Limit who can create, modify, or delete DNS records to prevent unauthorized changes.
Implement role-based access controls (RBAC) for DNS management.
Education and Awareness:
Educate your team about the risks associated with dangling DNS records and the importance of proper DNS management.
Provide training on how to identify and mitigate these risks.
Regular maintenance and vigilant monitoring are key to ensuring that your DNS infrastructure remains secure and resilient.
You can use a small tool i built do detect and build an inventory of dangling dns records: https://github.com/pgaijin66/dns-audit