Deep dive on PCI DSS 4.0 API Security Requirements

Shadow and Zombie APIs: How to Improve Your API Security

January 2, 2023

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

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