Introduction: The hidden risks of APIs you don’t see

APIs have become the backbone of modern applications, powering integrations, services, and digital growth. But not every API is visible to security teams. Many are undocumented, unmanaged, or long deprecated – yet still running. These hidden endpoints, known as shadow APIs and zombie APIs, create blind spots that attackers are quick to exploit.

The problem isn’t just technical. Hidden APIs increase compliance risk, inflate remediation costs, and undermine executive confidence. Gartner predicts that by 2026, 90% of organizations with APIs will have a federated team responsible for API quality. Without automated discovery, those teams risk overlooking critical endpoints that attackers can find first. The only way to control them is through continuous, automated discovery that identifies every active API, no matter where it lives.

Key takeaways

• Shadow APIs run in production without being undocumented, while zombie APIs are deprecated but still active.
• Both shadow and zombie APIs expand attack surfaces and create compliance blind spots.
• Manual discovery methods can’t reliably detect hidden APIs at scale.
• Invicti delivers automated discovery, validated vulnerability testing, and compliance-ready inventories.

What are shadow APIs?

Shadow APIs are undocumented or unmanaged endpoints that slip into production outside of governance. They often emerge from developer test environments, rushed releases, or poor documentation practices. In decentralized DevOps cultures, shadow APIs may even be intentionally deployed outside an official inventory process to move faster.

Risks: Shadow APIs expose organizations to attacks on endpoints no one remembers exist. They undermine compliance, making audits incomplete and risk reports inaccurate. They also create dangerous misalignment between what executives believe is secure and what is actually exposed.

Actionable advice: Prevent shadow APIs by integrating schema validation into CI/CD, enforcing design standards, and requiring governance checks for new APIs. This ensures hidden endpoints don’t bypass review before reaching production. Finally, run regular discovery to find active shadow APIs.

What are zombie APIs?

Zombie APIs are deprecated APIs that remain active in production despite being retired on paper. They typically linger due to weak lifecycle management, dependency on legacy systems, or lack of decommissioning enforcement. For example, when a new v2 API is deployed, v1 will often remain in production during a transition period to support legacy systems. If the transition is not carefully managed, v1 might stay live but forgotten indefinitely, becoming a zombie API.

Risks: Zombie APIs can run on outdated code and unpatched frameworks, leaving organizations vulnerable. Breaches have occurred where attackers exploited forgotten endpoints long after developers moved on. They are especially dangerous because they may still have access to internal systems and sensitive data but are invisible to most monitoring systems.

Actionable advice: Maintain a deprecation playbook. Track real usage through logs, notify dependent teams, and enforce shutdown timelines. Retiring APIs securely means testing during deprecation to confirm that no endpoints remain exposed. Finally, run regular discovery to find active zombie APIs.

Security and compliance risks of shadow and zombie APIs

Both shadow and zombie APIs increase risk in ways that extend beyond security teams:

• Expanded attack surface for attackers to exploit
• Data leaks from endpoints no one is monitoring
• Compliance blind spots that can cause audit failures
• Increased remediation costs after incidents

The business impact is just as critical as the technical one. This starts with compliance risks, as undocumented APIs can derail SOC 2, PCI-DSS, or HIPAA compliance efforts. Incident response becomes slower and more expensive when responders must first identify what system was actually attacked.

Why shadow and zombie APIs are hard to detect

Shadow and zombie APIs often remain hidden because organizations lack reliable visibility into their environments. Legacy systems rarely have accurate or complete API inventories, and manual discovery methods cannot keep up with sprawling hybrid and cloud infrastructures. As a result, many APIs slip through the cracks before security teams even know they exist.

The challenge is compounded by fragmented development practices. Siloed teams, shadow IT, and ad hoc deployments create governance blind spots where undocumented or outdated APIs persist. Older formats such as SOAP and XML may also go unnoticed if tools are tuned only for modern REST or JSON endpoints. These overlooked services can expose sensitive data or provide attackers with easy entry points.

Without automated discovery and monitoring, organizations are left guessing which APIs are active. That uncertainty creates opportunities for attackers, who thrive on unguarded and forgotten interfaces. The result is an expanding attack surface that is difficult to secure and easy to exploit.

Using automated discovery to uncover hidden APIs

The only scalable solution is to run automated discovery in a continuous process. API security on the Invicti Platform makes hidden APIs visible and manageable by combining discovery and scanning.

Continuous discovery across environments

Active endpoints are identified across on-premises, hybrid, and cloud environments. Multi-layered discovery maximizes the scope and effectiveness of discovery to make sure assets are not overlooked.

Agentless scanning for scale

With no agents required, discovery scales seamlessly across multi-cloud and hybrid infrastructures without adding friction. Note that discovery with network traffic analysis agents can also be set up as required to maximize effectiveness.

Proof-based vulnerability validation

Invicti’s proof-based scanning confirms which vulnerabilities are exploitable and delivers proof for issues that the scanner can exploit, greatly reducing false positives and enabling developers to fix what truly matters.

Compliance-ready inventory and reporting

With automated discovery, inventories are kept up to date, simplifying audits and providing governance-ready visibility for executives and boards. That way, hidden APIs stop being liabilities and become manageable, trackable assets.

Best practices to eliminate shadow and zombie APIs

Discovery and scanning automation is vital but only part of the answer. To prevent hidden APIs from persisting and then appearing in the first place, you need to:

1. Automate discovery across all your environments to ensure no API is missed.
2. Integrate discovery into CI/CD pipelines to catch emerging shadow APIs early in development.
3. Securely deprecate and retire old APIs and run testing to verify that zombie APIs are truly shut down.
4. Establish governance policies for lifecycle management to define ownership, SLAs, and accountability across Dev, Sec, and Ops.

Following these practices keeps API inventories accurate and risks under control.

Business benefits of API discovery

API discovery is not just a technical control but also a governance enabler and business safeguard. Organizations that uncover and eliminate shadow and zombie APIs realize significant business benefits:

• Reduced attack surface and fewer hidden risks
• Stronger compliance posture with accurate inventories
• Faster incident response when issues are detected
• Increased confidence for executives and boards in risk reporting
• Improved operational efficiency by eliminating duplicate or redundant APIs

Final thoughts on shadow and zombie API discovery

Shadow and zombie APIs are invisible threats that silently expand risk. Manual tracking can’t keep up with today’s API-driven ecosystems. Automated discovery provides the visibility, validation, and governance needed to eliminate blind spots and build executive trust.

Find shadow and zombie APIs in your environments with Invicti’s automated discovery and validated scanning. Get a demo of Invicti’s API discovery