...

AppSentinels named a leader and outperformer in 2025 GigaOm Radar for API Security – View the Report

LOGIN
Schedule a Demo
[rank_math_breadcrumb]

Shadow and Zombie APIs: How to Improve Your API Security

Picture of Apurva Prakash
Apurva Prakash
Marketing Manager @ AppSentinels
  • • ⏱︎10mins Read

APIs are everywhere, enabling businesses to maximize business value. From digital transformation and application modernization to cloud migration and microservices, API-first app architectures are finding their way into every technology touchpoint, giving rise to API sprawl. Consequently, most DevOps and security teams are uncertain about all the active and exposed APIs, and are lacking proper strategies to manage API sprawl. According to the Gartner’s 2022 security predictions, API security and management challenges organizations increasingly face in 2022 and beyond. As per the report, “by 2025, less than 50% of enterprise APIs will be managed, as explosive growth in APIs surpasses the capabilities of API management tools,” and “by 2025, the percentage of third-party APIs used in applications will average 30%, up from less than 10% in 2021, complicating dependency management.”

The incomplete visibility and management challenges due to explosive growth in APIs have led to the emergence of unwanted entities such as shadow APIs and zombie APIs. Malicious actors lurk for these APIs and exploit them to breach organizations and pilfer sensitive data or to take over accounts for financial gains.

So, how can you safeguard your organization from cybercriminals leveraging these vulnerable APIs to get into your network? In this blog, we help you understand in detail what these vulnerable APIs are and the API security best practices you need to protect your network:

What are shadow APIs?

Shadow APIs, sometimes referred as rogue APIs, are the APIs that exist and operate outside a company’s IT governance, management, and security frameworks. Shadow APIs are often created when developers bypass controls in order to release, update or deprecate APIs more quickly. For instance, a developer quickly builds and deploys an API to fix an immediate problem or a bug causing massive UX disruption or create an unauthorized or unrecognized API as proof of concept for a future project.

Whatever the reason, quickly deploying an API to accomplish an immediate task might be easy, but often translates to serious security concerns. In many ways, shadow APIs brings with them many of the similar challenges created by shadow IT. As security teams cannot protect the assets that are not properly documented, the shadow APIs lack proper security testing, monitoring, and protection. If an API endpoint has not been secured, it becomes a glaring vulnerability in a company’s tech scape, providing scope for attackers to leverage the vulnerable endpoints for conducting cyberattack.

Often, APIs deployed without the knowledge of security personnel tend to have vulnerabilities or misconfigurations, making it easier for third parties to steal enterprise data or compromise critical assets. Sometimes, shadow APIs are just formerly managed APIs copied to support other data paths without being documented. If attackers access older, unpatched API endpoints like these, they can easily infiltrate other services or trigger account takeovers.

What are Zombie APIs?

Simply put, zombie APIs are forgotten, outdated, or abandoned APIs. At one point, these APIs were valid, approved and served a function, but now they have been forsaken or replaced by newer versions. They have not been disabled or deprecated, but just left to wander in the application environment – hence, the term zombie.

Often, companies drive their focus on building their next feature and neglect the outdated, vulnerable endpoints. In many cases, businesses don’t have proper controls in place to version, deprecate, and sunset old APIs. So, these zombie APIs don’t receive any patching or maintenance from security standpoint, becoming a perfect opportunity for malicious actors to penetrate and access your most sensitive data repositories.

Another way for zombie APIs to emerge is through an organization’s dependence on a particular API version for integrating with other applications. If an outdated API is integral to supporting legacy versions of any software, developers may often hesitate to sunset or update it, in order to prevent any possible crash in functionality or connectivity. This would still be acceptable, except for the fact that security teams have to keep up with thousands of APIs, and tend to forget older ones, leaving them unprotected and unobserved. They linger within the application, but without maintenance and updating, which makes them vulnerable to infiltration tactics like brute force enumeration.

Light Up the Shadows: Best Practices to Identify and Protect Against Shadow & Zombie APIs

  • Automate API Documentation: Obviously, the best way is to prevent APIs from falling into the shadows in the first place. However, if developers have to manually update documentation at the end of each cycle, there’s huge possibility of improper documentation in a haste to complete the task. In order to prevent this manual error, you must configure the CI/CD pipeline to programmatically update documentation every time a change occurs, relieving developers from tedious, time-consuming documentation process.
  • Establish Standards for Updating New APIs: Implement a standard method for updating new APIs. For instance, the OpenAPI Specification helps you define API function before it is developed. By getting all stakeholders on the same page, you get team and organization-wide consensus on creating, releasing, monitoring and changing APIs.
  • Scan, detect and document all active APIs: Security teams are usually meticulous in monitoring and protecting mission-critical APIs. However, if third-party APIs are added for extra functions without necessary security review, or API endpoints are deployed with the intent of being documented later (but aren’t), you get shadow and zombie APIs. Select a tool that allows you to detect every single API endpoint (deployed at any point of time). The tool should provide perfect visibility into which APIs are live, where they are located and how they operate. It should also help identify any differences between what the API is programmed to do, and what it actually does.

Discover & Catalog All API Endpoints and Attributes with AppSentinels

AppSentinels continuously works to identify all APIs and their attributes and provide complete visibility into an organization’s API assets.

  • Comprehensive real-time API visibility: Real-time continuous discovery of all your APIs as and when they are deployed or modified. Our platform also delivers details on input and output parameters, data-types, whether a parameter is mandatory, optional, or PII/sensitive.
  • API Catalog: Consistently up-to-date and accurate API inventory even when an application is undergoing shifts.
  • Identification of API attributes: The platform provides deep insights into attributes about all API endpoints. Use this data to implement adequate security controls, depending on the attributes. Choose to allow shadow APIs, block forgotten APIs, or set up different rate-limits for admin APIs.
  • Application Risk Score: Get accurate data on the risk associated with each API in your application – its exposure, likelihood and impact. Additionally, monitor changes in risk as APIs evolve, and use this data to design appropriate responses to API-specific threats.Use AppSentinels’ vast and industry-best security mechanisms to detect, discover and defend your infrastructure against threats associated with shadow and zombie APIs. Monitor each API, its ability to access sensitive and PII data, and gain complete visibility of all endpoints that could put business-critical data at risk of exposure. Additionally, use API-specific data to align with governance standards and breeze through compliance audits.

Leverage AppSentinels API Security Platform to Protect Your Valuable APIs

Frequently Asked Questions

What is the difference between shadow APIs and zombie APIs, and why does this distinction matter?+–

Shadow APIs are endpoints that were never officially documented or registered in the organization’s API governance and created outside standard processes, unknown to security teams. Zombie APIs are endpoints that were officially deployed and documented but have since been deprecated or forgotten basically they’re in the history books but still actively accessible. The distinction matters because they require different remediation: shadow APIs need to be discovered, assessed, and either properly onboarded or removed; zombie APIs need to be identified in the existing inventory and actively decommissioned. Both are dangerous, but zombie APIs are particularly deceptive because they were once legitimate, making their continued existence seem less alarming.

What techniques do attackers use to discover shadow and zombie APIs that organizations themselves don’t monitor?+–

Attackers use exactly the same discovery techniques security teams should use but often don’t: subdomain enumeration via certificate transparency logs and DNS brute-forcing identifies shadow APIs on forgotten subdomains; port scanning and service discovery identifies APIs running on non-standard ports; web crawling and mobile app decompilation reveals undocumented endpoint references in application code; and Shodan-style internet scanning maps publicly accessible services. Attackers are often more systematic about API discovery than the organizations that own the APIs, which is precisely why shadow and zombie APIs remain such effective attack entry points despite the availability of defensive discovery techniques.

Why do zombie APIs typically retain their original broad permissions even after deprecation?+–

Zombie APIs retain broad permissions because formal deprecation in most organizations means removing the endpoint from documentation and stopping active maintenance and not actively reducing permissions or restricting access. Without an explicit decommissioning checklist that includes permissions review, the API continues to operate with whatever access grants were provisioned during its active lifecycle. Those permissions were often broad and granted to support multiple use cases and reducing them post-deprecation is seen as risky (might break something) without clear enough upside to prioritize. This makes zombie APIs doubly dangerous: accessible, unmaintained, and over-privileged.

What is the appropriate response when a zombie API is discovered in a production environment?+–

Upon discovering a zombie API, the appropriate response is: assess current traffic to determine if the endpoint still has legitimate users (some zombie APIs are still actively consumed without the owning team’s awareness); review access logs for suspicious access patterns that might indicate prior exploitation; immediately reduce permissions to the minimum necessary pending full assessment; engage with potential consumers to understand migration needs before hard removal; then execute a time-bounded deprecation: communicate decommission date, provide migration guidance, monitor for migration completion, and enforce hard shutdown rather than leaving the endpoint running indefinitely for non-migrated consumers.

How should organizations prioritize remediation when they discover dozens of shadow and zombie APIs simultaneously?+–

Prioritize by exploitability and impact: immediately address any discovered APIs that are externally accessible, unauthenticated, and handling sensitive data, these represent the highest risk and require urgent remediation or shutdown. Next priority: externally accessible authenticated APIs with sensitive data access that lack proper monitoring. Lower priority (but not ignored): internal-only APIs and those handling less sensitive data. Create a risk-tiered remediation backlog, assign ownership for each discovered API, set SLAs based on risk tier, and implement monitoring for all discovered endpoints even before full remediation, as detecting exploitation attempts while remediation is in progress provides critical early warning.

What processes should organizations put in place to prevent new shadow and zombie APIs from accumulating in the future?+–

Preventing future accumulation requires addressing both creation and lifecycle management. For creation: integrate API registration as a mandatory CI/CD gate before deployment reaches production, with automated scanning that flags unregistered deployments immediately. For lifecycle management: implement quarterly API lifecycle reviews for all registered APIs, assign explicit ownership with accountability for deprecation decisions, create formal deprecation checklists that include access restriction and monitoring shutdown steps, and set maximum active lifespan policies requiring explicit renewal decisions for long-running APIs. Together, these processes make shadow and zombie API accumulation the exception that triggers immediate alerts rather than the undiscovered background condition it currently is in most organizations.

Table of Contents

Related Content