The Hidden DNS Threat: How Dangling Records Are Creating Backdoors into Enterprise Networks

Executive Summary: DNS-based attack vectors have evolved far beyond traditional hijacking techniques, with 1.5 million DNS DDoS attacks occurring in Q1 of 2024 alone. While enterprises focus on perimeter security, a more insidious threat lurks in their DNS infrastructure: dangling records that create invisible backdoors for sophisticated attackers. Recent research reveals that 1.1 million CNAMEs are potentially vulnerable to takeover, while organizations have discovered 2,000+ exploitable DNS records in single audits. For security leaders managing external attack surfaces, understanding and mitigating DNS-based vulnerabilities has become mission-critical.

The Anatomy of a Modern DNS Attack Surface

In today's hyper-connected enterprise environment, DNS serves as more than a simple translation service—it's the invisible infrastructure that connects your organization to the digital world. Every subdomain, every CNAME record, and every forgotten cloud service creates potential attack vectors that skilled adversaries actively hunt and exploit.

The Expanding Digital Footprint Challenge

300+ New digital services deployed by organizations monthly

The number of exposed assets and data doubled in 2023, from 740,000 to 1.5 million TBs, while organizations today deploy more than 300 new digital services a month on average, contributing to a 32 percent rise in critical cloud exposures. This explosive growth creates a perfect storm where DNS misconfigurations multiply faster than security teams can discover and remediate them.

Consider this sobering reality: 79% of cyber risks are found outside a company's internal IT perimeter. Your carefully architected network security becomes irrelevant when attackers can simply walk through the front door using legitimate subdomains you've forgotten about.

The Trust Paradox

DNS-based attacks are particularly insidious because they exploit the fundamental trust relationship between your brand and your users. When attackers successfully claim a dangling subdomain like support.yourcompany.com, they inherit your organization's credibility. Users, browsers, and even automated systems treat malicious content hosted on your subdomain as legitimate—because technically, it is.

Dangling DNS: The Invisible Threat Vector

Understanding the Vulnerability

Dangling DNS records represent one of the most underestimated yet prevalent security risks facing modern enterprises. These are DNS entries that exist but point to resources no longer under your control—expired cloud services, deleted repositories, or decommissioned third-party integrations.

The Attack Sequence

A typical subdomain takeover follows this progression:

Service Integration: Your team creates blog.company.com pointing to company.ghost.com for a Ghost blog
Service Discontinuation: The Ghost subscription expires or the project is abandoned
DNS Neglect: The CNAME record remains active, still pointing to the non-existent Ghost instance
Attacker Registration: A threat actor claims company.ghost.com and hosts malicious content
Exploitation: Users visiting blog.company.com now reach attacker-controlled infrastructure

Real-World Scale and Impact

1.1M CNAMEs potentially vulnerable to takeover discovered in recent research

The scope of this problem is staggering. Microsoft discovered over 670 vulnerable subdomains in a single audit, while broader internet research shows that 21% of DNS records lead to unresolved content, and 63% of those throw '404 not found' errors.

Recent investigative research from October 2024 to January 2025 uncovered approximately 150 S3 buckets, previously owned by major corporations and government agencies, that were deleted but still referenced by outdated DNS records. Over 8 million requests were made to these non-existent buckets.

Advanced Attack Vectors

Supply Chain Infiltration

Modern subdomain takeovers extend far beyond simple website defacement. With organizations using subdomains to distribute software updates, cloud service templates, and other critical assets, an attacker could inject malicious code into these supply chains, leading to potential remote code execution (RCE), resource hijacking, or even persistent backdoors.

Email-Based Exploitation

Attackers can exploit dangling DNS by registering expired domains and adding SPF records to newly registered domains, enabling them to send email using your subdomain. This "SubdoMailing" technique bypasses traditional email security controls because the emails originate from technically legitimate DNS infrastructure.

Certificate Authority Bypass

A common misconception is that using SSL certificates protects your site from takeover. However, a threat actor can use the hijacked subdomain to apply for and receive a valid SSL certificate, granting them access to secure cookies and increasing the perceived legitimacy of malicious sites.

The Business Impact: Beyond Technical Metrics

Financial Consequences

$4.45M Average cost of a data breach in 2024

The financial implications of DNS-based attacks extend far beyond immediate technical remediation costs. The average breach now costs organizations $4.45 million per incident, while IDC study shows that each successful DNS attack costs businesses an average of $942,000.

These costs manifest across multiple dimensions:

Immediate Response: Emergency incident response, forensic analysis, and technical remediation
Business Disruption: Service downtime, lost productivity, and operational interruption
Regulatory Compliance: Potential fines and mandatory breach notifications
Brand Damage: Long-term reputation impact and customer trust erosion
Legal Liability: Potential lawsuits from affected customers and partners

Operational Disruption

DNS disruption could not only deny access to content but could also interfere with other systems, including spam defenses, cryptographic defenses (PKI), and inter-domain routing security (RPKI). When your DNS infrastructure becomes compromised, the ripple effects cascade through your entire operational ecosystem.

Case Study: When DNS Attacks Escalate

The Microsoft Example

Microsoft's experience illustrates the scale challenge facing large enterprises. Microsoft struggled with managing its thousands of subdomains, many of which were hijacked and used against users, its employees, or for showing spam content due to basic misconfigurations in their respective DNS entries.

This wasn't a case of sophisticated attackers exploiting zero-day vulnerabilities—it was simple DNS hygiene failures that created widespread security exposure across one of the world's most security-conscious organizations.

The Cloud Service Pattern

Security researchers have documented numerous cases where organizations using platforms like Ghost, Zendesk, or GitHub Pages for subdomains later abandoned these services without cleaning up DNS records. An attacker can leverage a free trial of Zendesk to take control of a help desk subdomain, with the attack scope expanding significantly if email forwarding still exists from the support subdomain to the Zendesk subdomain.

Detection and Prevention: A Comprehensive Strategy

Automated Discovery and Continuous Monitoring

The scale of modern DNS infrastructure demands automated approaches to vulnerability detection. Manual audits, while valuable, cannot keep pace with the rate of change in enterprise environments.

DNS Enumeration Techniques

Effective DNS security requires both passive and active enumeration strategies:

Passive Collection: Leveraging certificate transparency logs, search engines, and third-party databases
Active Scanning: Systematic probing of DNS infrastructure to identify dangling records
Continuous Monitoring: Real-time alerting when DNS configurations change or services become unavailable

Infrastructure Lifecycle Management

Provisioning Best Practices

The order of operations during service provisioning significantly impacts security exposure:

Claim Virtual Host First: Register with the service provider before creating DNS records
Verify Domain Ownership: Implement domain verification processes where available
Document Dependencies: Maintain comprehensive records of external service relationships
Create DNS Records Last: Add CNAME or other records only after confirming service availability

Decommissioning Protocols

Preventing subdomain takeovers is a matter of order of operations in lifecycle management—remove DNS records first when deprovisioning services. This simple process change eliminates the window of vulnerability that attackers exploit.

The External Attack Surface Management Solution

Why Traditional Security Fails

Traditional perimeter-based security models assume clear boundaries between "inside" and "outside" your network. DNS-based attacks obliterate these boundaries by exploiting the trust relationships that extend far beyond your managed infrastructure.

The Visibility Challenge

Unknown subdomains can be challenging, as they are not always closely monitored. When the service which points to the subdomain expires or is forgotten, they become a potential foothold or entry point for attackers. You can't protect what you can't see, and the exponential growth of external digital assets makes comprehensive visibility increasingly difficult.

The EASM Advantage

External Attack Surface Management (EASM) addresses DNS vulnerabilities through a fundamentally different approach: continuous discovery and monitoring of your organization's internet-facing assets from an attacker's perspective.

Comprehensive Asset Discovery

Modern EASM platforms like Vantage employ multiple discovery techniques to build complete asset inventories:

DNS Enumeration: Systematic scanning of DNS records and subdomain relationships
Certificate Transparency Mining: Analyzing CT logs for undiscovered subdomains
Third-Party Integration Tracking: Identifying external service dependencies
Shadow IT Detection: Discovering unauthorized cloud services and domain registrations

Real-Time Risk Assessment

Unlike point-in-time security assessments, EASM provides continuous monitoring that adapts to your changing infrastructure. When a cloud service expires or a subdomain becomes dangling, you receive immediate alerts with actionable remediation guidance.

Threat Intelligence Integration

Leading EASM platforms integrate threat intelligence to identify when your assets are being actively targeted or have already been compromised. This proactive approach enables prevention rather than reactive incident response.

The Strategic Imperative: DNS Security as Business Enablement

Market Context and Urgency

$6.55B Projected EASM market size by 2029, growing at 33.5% CAGR

The External Attack Surface Management market is experiencing explosive growth, projected to reach $6.55 billion by 2029, growing at a 33.5% CAGR from 2024 to 2029. This growth reflects not just vendor success, but fundamental changes in how organizations must approach cybersecurity in an increasingly connected world.

Industry Recognition

88% of organizations have experienced one or more DNS attacks on their network, with an average of seven per year. The ubiquity of DNS-based attacks has moved them from edge cases to core security concerns that every enterprise must address.

Competitive Advantage Through Proactive Security

Organizations that implement comprehensive DNS security gain significant competitive advantages:

Customer Trust: Demonstrating proactive security measures builds customer confidence and can become a competitive differentiator
Operational Resilience: Reducing attack surface exposure minimizes business disruption and enables more reliable service delivery
Regulatory Compliance: Proactive compliance with emerging security requirements avoids reactive scrambling when new regulations emerge
Cost Optimization: Preventing incidents is significantly more cost-effective than responding to breaches

How Vantage Solves the DNS Security Challenge

Comprehensive External Attack Surface Visibility

Vantage's EASM platform addresses DNS vulnerabilities through continuous discovery and monitoring that provides unprecedented visibility into your organization's external attack surface. Our approach combines automated asset discovery with deep DNS analysis to identify dangling records, misconfigurations, and potential takeover targets before attackers can exploit them.

Advanced Discovery Capabilities

Multi-Source Intelligence: Leveraging certificate transparency logs, DNS databases, and threat intelligence feeds
Automated Subdomain Enumeration: Continuous scanning that adapts to organizational changes
Third-Party Service Mapping: Identifying external dependencies and integration risks
Historical Analysis: Understanding DNS evolution patterns to predict future risks

Real-Time Risk Assessment and Prioritization

Our platform doesn't just discover vulnerabilities—it provides the context and prioritization that security teams need to focus their efforts effectively. By combining technical vulnerability data with business impact analysis, Vantage enables strategic risk management rather than reactive patching.

Intelligent Risk Scoring

Business impact assessment based on asset criticality and exposure
Threat intelligence integration for active targeting indicators
Exploitability analysis that considers real-world attack patterns
Trend analysis that identifies increasing risk trajectories

Actionable Remediation Guidance

Vantage transforms vulnerability data into concrete action plans that development and operations teams can execute immediately. Our platform provides specific remediation steps, technical guidance, and verification methods for each identified issue.

Streamlined Remediation

Step-by-step remediation instructions tailored to specific DNS configurations
Integration with popular DNS management platforms for automated fixes
Verification testing to confirm successful vulnerability resolution
Change tracking to prevent regression and ensure continuous improvement