Stale DNS Entry

In cybersecurity, a stale DNS entry (also known as a "dangling" or "orphaned" DNS record) is a Domain Name System configuration that points to a resource (such as a server, website, or service) that is no longer active, available, or under the control of its original owner.

This often occurs when:

• Services are decommissioned: When a company shuts down a service or application, the corresponding DNS record is not removed or updated.

• Migrations happen: A service moves to a new platform or IP address, but the old DNS record remains.

• Domains expire: A domain name expires and is no longer owned by the original entity, but a subdomain's DNS record (e.g., test.example.com) still points to a resource that was associated with the now-expired domain.

• Cloud resources are deprovisioned: Virtual machines or other cloud resources are terminated, but their DNS entries persist.

Cybersecurity Risks of Stale DNS Entries

Stale DNS entries pose significant cybersecurity risks because they can be exploited by malicious actors, primarily through techniques such as subdomain takeover or IP-use-after-free attacks.

Here's how they can be exploited and their impact:

1. Subdomain Takeover:

   • The Vulnerability: If a DNS record for a subdomain (e.g., blog.example.com) points to a service (like a cloud storage bucket, a defunct SaaS platform, or an old server) that the organization no longer controls, an attacker can register or claim that abandoned resource.

   • The Exploit: Once the attacker controls the resource, the stale DNS record directs legitimate traffic for the subdomain to the attacker's newly controlled environment.

   • Consequences:

     • Phishing: The attacker can set up a fake website that mimics the legitimate one, stealing user credentials or other sensitive information.

     • Malware Distribution: The attacker can host malware or malicious scripts, infecting visitors who access the compromised subdomain unwittingly.

     • Brand Damage: The organization's reputation can be severely harmed by malicious activity on what appears to be its legitimate subdomain.

     • Bypassing Security Controls: If the attacker can control MX records, a compromised subdomain can be used to bypass security measures like email authentication (e.g., SPF, DKIM, DMARC) in some cases.

     • Data Leaks: If the stale record pointed to a resource that once held sensitive data, and that resource becomes reclaimable, attackers could potentially access that data.

2. IP-Use-After-Free Attacks:

   • The Vulnerability: This occurs when a DNS record points to an IP address that an organization no longer uses or has released (e.g., a dynamic IP from a cloud provider).

   • The Exploit: An attacker can allocate that specific IP address for their malicious server. Since the stale DNS record still points to that IP, legitimate traffic for the domain or subdomain is directed to the attacker's server.

   • Consequences: Similar to subdomain takeovers, this can lead to phishing, malware distribution, and brand damage. It also allows attackers to gain valid TLS/SSL certificates for the domain, making their malicious site appear legitimate to users.

Why Stale DNS Entries are a Problem

• Hidden Vulnerabilities: Stale entries are often overlooked, as "dark assets" on an organization's external attack surface. They can persist for long periods without detection.

• Exploitation Simplicity: Once a stale record is identified, subdomain takeovers and IP-use-after-free attacks are often relatively easy for attackers to execute.

• Trust Exploitation: Users inherently trust an organization's domain name. When a stale record redirects them to an attacker-controlled site, that trust is exploited.

Mitigation

To mitigate the risks associated with stale DNS entries, organizations should:

• Implement Regular DNS Audits: Periodically review and inspect all DNS records to identify any that point to resources no longer in use or under control.

• Use DNS Scavenging (for dynamic DNS): Configure DNS servers to remove outdated or unrefreshed dynamic DNS records automatically.

• Establish Clear Decommissioning Procedures: When services or resources are taken offline or migrated, ensure that all associated DNS records are promptly removed or updated as part of the decommissioning process.

• Monitor for Expired Domains and Subdomains: Track domain expiration dates and monitor for any subdomains that might become vulnerable.

• Leverage External Attack Surface Management (EASM) Tools. These tools can help discover and monitor all publicly exposed assets, including stale DNS records, that attackers could exploit.

ThreatNG offers a comprehensive solution for managing external attack surface, digital risk, and security ratings, which would significantly help address the issue of stale DNS entries and the associated cybersecurity risks, particularly subdomain takeovers.

Here's how ThreatNG would help, highlighting its key capabilities:

External Discovery

ThreatNG excels at external discovery, performing purely external, unauthenticated discovery without the need for connectors. This is crucial for identifying stale DNS entries because it means ThreatNG can scan the internet for an organization's digital assets from an attacker's perspective. It will find subdomains and DNS records that might have been forgotten or are no longer actively managed, even if they aren't directly linked to active internal systems.

External Assessment

ThreatNG provides detailed external assessment ratings that directly address the risks posed by stale DNS entries:

• Subdomain Takeover Susceptibility: ThreatNG evaluates a website's susceptibility to subdomain takeover. It uses external attack surface and digital risk intelligence, incorporating Domain Intelligence, to perform this assessment. This includes comprehensively analyzing the website's subdomains, DNS records, and other relevant factors. By analyzing these elements, ThreatNG can pinpoint subdomains with DNS records pointing to unowned or abandoned resources, prime targets for takeover. For example, if dev.example.com still has a CNAME record pointing to a decommissioned Heroku app, ThreatNG would flag this as a high subdomain takeover susceptibility.

• Web Application Hijack Susceptibility: This score is substantiated by analyzing external web application components to identify potential entry points for attackers. A stale DNS entry leading to an attacker-controlled page could be considered a "hijacked" part of the web application, making this score relevant.

• Brand Damage Susceptibility: Stale DNS entries leading to subdomain takeovers can result in phishing sites or malicious content being hosted on what appears to be a legitimate part of an organization's domain, directly damaging the brand. ThreatNG's assessment factors in Domain Intelligence would help identify such vulnerabilities.

• Data Leak Susceptibility: A data leak could occur if a stale DNS entry points to a reclaimable cloud storage bucket that once held sensitive data. ThreatNG's assessment considers Cloud and SaaS Exposure and Domain Intelligence to determine data leak susceptibility.

• Cyber Risk Exposure: ThreatNG's Domain Intelligence module covers parameters like certificates, subdomain headers, vulnerabilities, and sensitive ports. A stale DNS entry that directs traffic to an insecure or compromised resource would directly contribute to an organization's overall cyber risk exposure.

Reporting

ThreatNG offers various reports, including Security Ratings, Inventory, and Prioritized reports (High, Medium, Low, and Informational). For stale DNS entries, these reports would provide:

• Prioritized Risks: Identify and prioritize stale DNS entries based on their potential impact (e.g., a subdomain highly susceptible to takeover might be flagged as "High" risk).

• Inventory: Provide a detailed inventory of all discovered DNS records and subdomains, making tracking and managing them easier.

• Security Ratings: These ratings reflect the impact of stale DNS entries on the overall security posture, providing a clear metric for management.

• Recommendations: The embedded Knowledgebase within reports would offer practical advice and guidance on remediating identified stale DNS entries, enabling proactive measures to improve security posture. For instance, it might recommend removing the DNS record, updating it to a legitimate resource, or taking ownership of the abandoned cloud service.

Continuous Monitoring

ThreatNG continuously monitors all organizations' external attack surface, digital risk, and security ratings. This is paramount for addressing stale DNS entries, as:

• It ensures that new stale DNS entries, which can emerge as services are decommissioned or migrated, are quickly identified.

• It verifies that remediation efforts for existing stale entries have been successful and that the vulnerability no longer exists.

• Continuous monitoring can quickly detect changes and alert the organization if an attacker takes over a subdomain through a stale entry.

Investigation Modules

ThreatNG's investigation modules provide deep insights that are invaluable for understanding and addressing stale DNS entries:

• Domain Intelligence: This module is central to identifying stale DNS entries.

  • DNS Intelligence: Provides Domain Record Analysis, including IP Identification, Vendors, and Technology Identification. This would reveal if a DNS record points to an IP address or a technology no longer in use or owned by the organization. It also includes Domain Name Permutations, which can help identify potentially malicious look-alike domains that might be set up to exploit trust.

  • Subdomain Intelligence: This is critical. It evaluates Subdomain Takeover Susceptibility directly. It also provides HTTP Responses, Header Analysis (Security Headers and Deprecated Headers), Server Headers (Technologies), and Cloud Hosting information (AWS, Microsoft Azure, Google Cloud Platform, Heroku, Pantheon, Vercel). If a subdomain's DNS points to an IP address belonging to an attacker or a cloud service the organization no longer controls, this module will highlight it. For example, if test.example.com has an HTTP 200 response, but the server headers indicate it's hosted on an unexpected cloud provider or a generic landing page service that the organization doesn't use; it could signal a stale DNS entry leading to a takeover.

• IP Intelligence: This module identifies IPs, Shared IPs, ASNs, and Country Locations. If a DNS record points to an IP address not within the organization's expected IP ranges or is associated with a different ASN, it could indicate a stale entry or an IP-use-after-free vulnerability.

• Certificate Intelligence: By analyzing TLS Certificates (Status, Issuers, Active, Certs without Subdomains, Subdomains without Certificates), ThreatNG can identify if a subdomain has an SSL certificate issued for it but points to a resource that is not under the organization's control. This could indicate a successful subdomain takeover where the attacker obtained a valid certificate for the compromised subdomain.

Intelligence Repositories (DarCache)

ThreatNG's DarCache intelligence repositories provide contextual data that enhances the understanding of stale DNS entry risks:

• Dark Web (DarCache Dark Web) and Compromised Credentials (DarCache Rupture): While not directly identifying stale DNS entries, if an organization's compromised credentials are found, an attacker could potentially use them to manipulate DNS records, highlighting the importance of overall security posture in preventing such issues.

• Vulnerabilities (DarCache Vulnerability): This repository includes NVD, EPSS, and KEV data. While not directly related to stale DNS, the overall risk posture is compounded if a stale DNS entry directs to a server with known vulnerabilities. ThreatNG helps prioritize such vulnerabilities by understanding their real-world exploitability and likelihood of exploitation.

• SEC Form 8-Ks (DarCache 8-K): Relevant if a breach or incident related to a stale DNS entry had to be publicly disclosed, allowing for historical context.

Complementary Solutions

ThreatNG's capabilities can be significantly enhanced by working in synergy with complementary solutions:

• Security Information and Event Management (SIEM) Systems: ThreatNG's continuous monitoring and reporting capabilities would feed valuable external threat intelligence, including alerts on potential subdomain takeovers or suspicious DNS changes, directly into a SIEM system. For example, if ThreatNG detects a change in the IP address associated with a critical subdomain and flags it as high risk, the SIEM could correlate this with internal network logs or user activity to identify potential malicious access or data exfiltration attempts.

• Security Orchestration, Automation, and Response (SOAR) Platforms: When ThreatNG identifies a stale DNS entry highly susceptible to takeover, a SOAR platform could automate a series of actions. This could include automatically generating a high-priority ticket for the IT team, initiating a workflow to verify the ownership of the pointed-to resource, or even triggering a block on external traffic to the identified IP if it's confirmed to be malicious.

• Brand Protection and Anti-Phishing Services: ThreatNG's ability to identify subdomain takeover susceptibility and derive BEC & Phishing Susceptibility through Domain Intelligence makes it an excellent partner for brand protection solutions. If ThreatNG flags a highly vulnerable subdomain, a brand protection service could proactively monitor for attacker attempts to register similar-looking domains or set up phishing campaigns. If a takeover occurs, the combined solution can rapidly issue takedown requests. For instance, if support.example.com is flagged as vulnerable, the brand protection solution can specifically watch for phishing sites using variations like support-example.com.

• Threat Intelligence Platforms (TIPs): ThreatNG's extensive DarCache intelligence repositories, covering Dark Web, Compromised Credentials, Ransomware, and Vulnerabilities, can enrich a TIP. The TIP can then provide a broader context by integrating ThreatNG's findings with other threat feeds, allowing security teams to understand if a detected stale DNS entry is part of a larger, ongoing threat campaign targeting similar vulnerabilities.

• Vulnerability Management Solutions: While ThreatNG identifies known vulnerabilities through DarCache Vulnerability, a dedicated vulnerability management solution can go deeper into internal scanning and patching. The external perspective from ThreatNG, particularly on exposed sensitive ports or IPs due to stale DNS, can inform and prioritize the vulnerability management tool's internal scanning efforts, ensuring the most exposed vulnerabilities are addressed first.

ThreatNG provides the crucial external visibility and assessment required to identify and understand the risks of stale DNS entries. Its continuous monitoring, detailed reporting, and deep investigation modules empower organizations to detect these hidden vulnerabilities and take proactive steps to prevent subdomain takeovers and associated attacks. When combined with complementary security solutions, the insights from ThreatNG can be acted upon more rapidly and effectively, creating a more robust defense against external threats.