What are shadow APIs?

Shadow APIs are application programming interfaces that exist in a company’s environment but are not properly tracked, documented, or managed by the security team. They often appear when developers launch new features, test integrations, or connect third-party tools faster than internal governance can keep up.

The paper Security Concerns in Android mHealth Apps, a large-scale analysis of more than 20,000 mHealth apps, found that many still used unencrypted communication and exposed sensitive data over unsecured traffic. The study substantiated this when it said, “mHealth apps make widespread use of unsecured Internet communications and third party servers.”

Shadow APIs are unmanaged doorways into systems that may contain protected health information (PHI) but lack the same authentication, monitoring, and lifecycle controls as permitted APIs.

How shadow APIs are created

When companies introduce new digital services faster than their governance can keep up, they often establish shadow APIs.That happens when teams connect mobile apps, cloud platforms, external sensors, third-party APIs, and provider systems to move data faster and improve interoperability, while documentation, ownership, and security review lag behind. An Emperical Software Engineering study of 27 top-ranked mental health apps, which found that 20 of the 27 apps were at security risk and 4 more were at high risk.

The same study found that 68% of the apps exposed API keys used to access third-party services, 79% stored data in plain text in files or databases, and only 3 of the 27 developers said they had conducted a Privacy Impact Assessment. Researchers also found that apps relied heavily on third parties for marketing, advertising, cloud services, and payments.

Healthcare organizations also have to deal with mapping, migration, maintenance, and standards complexity. Growth makes it easy for an endpoint designed for integration, testing, or a temporary procedure to be operational without clear ownership or regular evaluation.

Shadow APIs vs other hidden API problems

The primary difference is that shadow APIs are at first a problem with visibility and governance, while other API concerns are usually security or implementation vulnerabilities in APIs that teams already know about. Exposing sensitive health information can happen through API flaws, sharing data with third parties, using weak cryptography, and leaking personal information and credentials. A common API problem might be weak authentication, bad encryption, or an insecure coding choice in a system that the organization already knows about.

For healthcare organizations, that distinction matters even when they use secure communication platforms like Paubox, because protecting known email and messaging channels does not automatically address unknown or unmanaged interfaces elsewhere in the environment.

A shadow API problem, on the other hand, starts earlier because the interface itself might not be fully inventoried, clearly owned, or regularly reviewed. A JMIR mHealth and uHealth review found that secure development is often hindered by a lack of security guidelines and regulations, developers’ lack of knowledge and expertise, and a lack of security testing, all of which make it easier for unmanaged interfaces to remain active longer than they should.

The review identified these as recurring barriers across the literature, with lack of security guidelines and regulations appearing in 63% of included studies and developers’ lack of knowledge and expertise appearing in 56%. That difference is notable as teams can usually fix a known API bug faster than they can protect an interface they cannot see completely.

How attackers find and exploit shadow APIs

Attackers first hunt for missed interfaces by looking at program code, network traffic, logs, generated data, internet interactions, and links to third parties. These areas can show hidden endpoints and backend services that are not effectively managed.

One AMIA study captures the risk: “The nature of communications technology and mobile computing exposes many new attack surfaces to the outside world.” Once attackers find those interfaces, they can test them for common weaknesses and exploit whatever security gaps they uncover.

How organizations can discover shadow APIs

Paubox’s Email API includes audit logging, reporting, and webhook-based visibility into email transactions, so it can help a team identify undocumented or poorly governed integrations that already route messages through Paubox-managed workflows. It helps with mitigation by encrypting email messages, keeping audit trails, and providing archiving and access-control measures that make it easier to analyze and look into sensitive data flows.

The Inbound Security uses generative AI that takes care of analysis, filtering, and rules-based controls to protect against phishing, malware, ransomware, and spoofing. Attackers are therefore less likely to use email as the first step to abuse an unmanaged interface somewhere else in the environment.

See also: HIPAA Compliant Email: The Definitive Guide (2026 Update)

FAQs

What role do SPF, DKIM, and DMARC play in inbound email security?

These email authentication standards help verify whether a message really comes from the domain it claims to come from and reduce spoofing risk.

Does inbound email security scan attachments and links?

Yes, many solutions inspect attachments for malware and analyze links for known malicious destinations or suspicious behavior.

What does an API request include?

An API request often includes an endpoint, a method such as GET or POST, headers, authentication details, and sometimes a body with data.

What is an endpoint in an API?

An endpoint is the specific URL or location where a request is sent to access a resource or perform a function.