In API security, one of the least visible and most dangerous issues today is the prevalence of Shadow APIs. Understanding the threats posed by these hidden APIs is critical for those new to API security research and testing. 

They can easily slip under the radar of even the most diligent security teams, providing a clear path for threat actors to infiltrate systems and compromise sensitive data. This post explores Shadow APIs, their security risks, and how to start defending against them.

What are Shadow APIs?

Simply put, Shadow APIs are undocumented or unknown APIs that exist within a company’s infrastructure but aren’t accounted for in official documentation. 

Often, they are the result of rapid development cycles, where APIs are created for internal testing, proof of concept, or development purposes but aren’t adequately documented or maintained. 

Sometimes, they’re legacy APIs no one realized were still active after a service or application evolved. In either case, these APIs become “shadows,” existing out of sight of the main API catalog that development and security teams are aware of.

These hidden APIs can quickly turn into a vulnerability because if no one is aware of them, no one is actively monitoring or securing them. For organizations dealing with extensive or complex API architectures, this can lead to significant security exposure, often without anyone realizing it until it’s too late.

Why Shadow APIs are Vulnerable

Shadow APIs are vulnerable for several reasons, all stemming from a fundamental lack of visibility and oversight. Here are some of the main reasons why Shadow APIs pose such a security risk…

Lack of Visibility

If security teams can’t see these APIs, they can’t protect them. Shadow APIs go unnoticed because they don’t show up in the API documentation that security teams use to track assets. This “out of sight, out of mind” scenario means potential vulnerabilities remain unchecked and unpatched.

Absence of Monitoring and Updates

Since Shadow APIs aren’t officially acknowledged, they don’t usually receive the same updates, patches, or security fixes that well-documented APIs do. They’re left behind in the security update cycle, making them prime targets for attackers. 

Additionally, if no one is logging activity on these APIs, it’s nearly impossible to detect if they’re being accessed by unauthorized users or manipulated by threat actors.

Insecure Practices in Development

APIs created outside the standard security review process are more likely to have flaws. In many cases, Shadow APIs are developed with quick-and-dirty methods, as their primary purpose may have been testing or temporary use. As a result, these APIs may have hard-coded credentials, weak access controls, or even no authentication at all.

Real-World Risks of Shadow APIs

Shadow APIs aren’t just theoretical vulnerabilities. They’ve led to real-world data breaches and security incidents, costing companies millions of dollars and damaging their reputations. Here are a few examples of how Shadow APIs can lead to serious issues:

• Exposing Sensitive Data: When Shadow APIs aren’t secured, they can expose sensitive data like user information, payment details, and internal records. This data exposure can violate data privacy regulations, leading to financial penalties and customer distrust.
• Undermining Compliance: Many industries have strict compliance requirements, and undocumented APIs can lead to accidental compliance violations. Regulatory bodies require companies to account for every endpoint that could expose or process sensitive data.
• Access Control Failures: Shadow APIs often lack the access controls in place for primary APIs. Unauthorized access to these APIs can give attackers a foothold in the organization, potentially leading to deeper infiltration and even lateral movement to other critical systems.

How Your Adversaries Exploit Shadow APIs

Understanding how threat actors exploit Shadow APIs is essential to appreciate the risk they pose. Typically, attackers will use several techniques to discover and manipulate these APIs. 

Let’s look at a few of them.

1. Endpoint Brute-Forcing

Attackers may try to bruteforce API endpoints by guessing likely names or structures. This technique can reveal undocumented or legacy APIs that were not adequately hidden or protected. 

I’ve shown you how to do that in the past in my article on Finding Hidden API Endpoints Using Path Prediction.

2. Default or Weak Configurations

Since Shadow APIs often bypass security best practices, attackers can exploit weak or default settings. They might find that authentication isn’t enforced or that the API allows broader access than expected.

I’ve shown you how to detect that by automating your API hacking with Burp extensions like Autorize. And I’ve shown you how to find access control issues because of this weak config as well.

3. Public Repositories and Code Scraping

Sometimes, information about Shadow APIs is inadvertently leaked through public repositories, forums, or documentation sites. Attackers comb through these resources to find endpoints that might still be accessible but unprotected.

I’ve also shown you how you can scrape mobile apps in a similar manner. Like my article on Discovering API secrets & endpoints using APKLeaks.

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By exploiting Shadow APIs with these techniques, attackers can gain unauthorized access to data and systems, bypassing the security measures applied to the primary, well-documented APIs. This exploitation can lead to severe security breaches and significant financial and reputational damage.

Defensive Strategies Against Shadow API Risks

Mitigating the risks associated with Shadow APIs requires a proactive and structured approach. Below are some of the key strategies that can help organizations secure their API environments and reduce the attack surface associated with Shadow APIs.

1. API Inventory

One of the most critical steps is to maintain a comprehensive API inventory. This inventory should list every API endpoint, including those created for testing, temporary projects, or internal use. An accurate inventory allows security teams to monitor, update, and secure each API, reducing the chance that a Shadow API will slip through the cracks.

2. Regular Security Audits

Regular API security audits can help identify undocumented or forgotten APIs. These audits should involve a combination of automated scanning and manual testing to detect any APIs that may have been overlooked during initial assessments.

3. Automated Discovery Tools

There are various tools available that can help automate the discovery of Shadow APIs. API management solutions, network scanning tools, and even AI-driven anomaly detection tools can identify suspicious traffic patterns or unknown endpoints within the network. These tools make it easier for security teams to uncover hidden APIs and assess their security posture.

4. Implementing Logging and Monitoring

Once an API inventory is established, every API should have comprehensive logging and monitoring in place. This monitoring allows teams to detect any unauthorized or unusual activity. Ideally, the logging should be integrated into a centralized security information and event management (SIEM) system, so alerts can be generated if anomalies occur.

5. Enforce Secure Development Practices

Developers should follow security best practices, even for APIs created as “temporary” or “internal” endpoints. By enforcing secure coding practices across all APIs, organizations can reduce the chances that Shadow APIs will become easy targets. This includes using strong authentication, proper access controls, and avoiding hard-coded secrets or default settings.

Conclusion

Shadow APIs present a unique and significant challenge in the realm of API security. These undocumented and unmonitored endpoints can offer a direct path for threat actors into an organization’s systems, leaving sensitive data exposed and compliance efforts undermined. 

By understanding what Shadow APIs are, why they’re vulnerable, and how attackers exploit them, security professionals—especially those new to API security—can better protect their organizations.

Securing Shadow APIs requires a proactive approach, including maintaining an API inventory, conducting regular security audits, leveraging automated discovery tools, and enforcing secure development practices. Remember, keeping Shadow APIs secure is an ongoing effort that requires awareness and vigilance from everyone involved in API development and security.

For those new to API security, tackling Shadow APIs is an important step in building a robust security posture and staying one step ahead of threat actors constantly looking for exposed, unmonitored vulnerabilities.

One last thing…

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The post Why Shadow APIs provide a defenseless path for threat actors appeared first on Dana Epp's Blog.

*** This is a Security Bloggers Network syndicated blog from Dana Epp's Blog authored by Dana Epp. Read the original post at: https://danaepp.com/why-shadow-apis-provide-a-defenseless-path-for-threat-actors