Zombie APIs: The Undead Threat to Your Security
Zombie APIs, sometimes called “orphaned” or “forgotten” APIs, refer to endpoints that were initially deployed for a specific purpose but are no longer actively used or maintained. These APIs are often left operational within an organization’s infrastructure due to oversight or incomplete decommissioning processes. Despite their inactivity, zombie APIs can still expose sensitive data, provide unauthorized access, or contain vulnerabilities that attackers exploit, making them a silent threat within the API landscape.
As organizations adopt agile workflows and expand their digital ecosystems, zombie APIs become increasingly common, especially when new endpoints are developed rapidly, and older ones are abandoned. This brief explores the risks posed by zombie APIs, real-world consequences of leaving them unaddressed, and effective strategies for identifying and mitigating these threats.
The Security Risk of Zombie APIs
Zombie APIs pose significant security risks for organizations. In fact, the Salt Security State of API Security report showed Zombie APIs as the number one API security concern for organizations over the past four surveys. Worryingly, many traditional tools and practices are unable to detect, secure and govern against. The risks posed include:
1. Outdated Security Protocols and Vulnerabilities
Unlike actively used APIs, zombie APIs often lack routine security updates. As these APIs are left out of regular maintenance cycles, they frequently use outdated authentication protocols, encryption standards, or access controls, making them vulnerable to attacks.
Without up-to-date security measures, zombie APIs become easy targets for attackers who scan for endpoints using deprecated protocols, such as older versions of TLS, or simpler authentication methods like API keys. Attackers exploit these weak points to gain unauthorized access to sensitive systems, data, or even broader network controls.
For example, in 2023, major telecommunications provider T-Mobile experienced a breach when attackers exploited a zombie API that used outdated TLS encryption. The API had been used for a legacy mobile app, and due to a lack of monitoring and updates, the obsolete encryption made it easy for attackers to intercept and decrypt data.
Action: Regularly scan all APIs for deprecated protocols or outdated configurations. Automated security assessments should include identifying inactive APIs that lack recent updates, allowing security teams to either decommission them or bring them up to current standards.
2. Unmonitored Data Exposure and Privacy Risks
Many APIs transmit or access sensitive data, but when an API becomes inactive and is left unmonitored, it may expose data unintentionally. In regulated industries, unmonitored data exposure can lead to compliance violations and costly fines.
For example, in 2018 an API flaw within the United States Postal Service (USPS) potentially exposed the data of 60 million customers. The vulnerability allowed anyone with a USPS account to access other users' sensitive information, including email addresses, usernames, street addresses, and phone numbers. The flaw was discovered and reported months prior, but it wasn't until a security researcher contacted Brian Krebs that the USPS took action to address the issue.
Action: Integrate data loss prevention (DLP) tools into API monitoring systems to flag abnormal data exposure. Continuous monitoring should extend to inactive APIs, and regular audits should be conducted to ensure sensitive data is protected or access is completely shut down.
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Download Report3. Compliance Violations from Lack of Documentation and Monitoring
Zombie APIs are often undocumented or improperly cataloged, creating significant compliance risks. For regulations like GDPR, CCPA, or HIPAA, organizations must be able to account for all systems handling sensitive data. When an API is left undocumented, it becomes impossible to verify its compliance status, posing a risk for regulatory breaches.
As organizations expand their API ecosystems, managing compliance for every endpoint becomes challenging, especially for shadow and zombie APIs. Zombie APIs often fall outside of regular compliance checks, increasing the risk of non-compliance and potential fines.
The 2021 T-Mobile data breach is a good example of an API-related attack that led to compliance violations. While the exact details of the attack haven't been fully disclosed, it's believed that hackers exploited vulnerabilities in T-Mobile's API to gain unauthorized access to sensitive customer data, including personal information, Social Security numbers, and financial details. This breach resulted in significant regulatory fines and reputational damage for T-Mobile.
Action: Regular API audits and documentation practices are critical for compliance. Automated discovery tools can help map all APIs within an organization, ensuring every endpoint is documented, monitored, and assessed for compliance with industry standards.
4. Attackers’ Preferred Entry Points for Lateral Movement
Attackers frequently seek out forgotten or unmonitored endpoints because they are less likely to be detected and often use weaker security settings. Once inside, attackers use these entry points for lateral movement within an organization’s network, expanding access beyond the original API.
Once attackers gain entry through a vulnerable API, they can access interconnected systems, extract sensitive data, and potentially escalate their privileges. Zombie APIs, especially those with weak authentication or access controls, provide easy access for attackers to explore internal systems without detection.
The Salt Security 2024 State of API Security Report found that APIs were increasingly being used by cybercriminals as an entry point for cyberattacks. The report found that over 37% of respondents reported experiencing an API security incident in the past year, compared to 17% in 2023, with the count of APIs increasing by 167% in the past year. Additionally, the report found that many organizations lack a mature API security strategy, leading to increased risks and vulnerabilities.
Action: Implement strict access control and monitoring protocols across all APIs, including inactive ones. Network segmentation and micro-segmentation help limit lateral movement, preventing attackers from using zombie APIs to access sensitive systems.
Addressing the Zombie API Threat Now
Proper API lifecycle management involves tracking each API from development through deprecation and decommissioning. Without a formalized process, APIs may remain active long after their purpose has ended, becoming zombie APIs. Establishing a rigorous lifecycle management policy ensures that outdated APIs are not left vulnerable in production environments.
A clear lifecycle policy requires teams to document every API, schedule regular reviews, and deactivate APIs that are no longer needed. By enforcing this process, organizations can reduce API sprawl, minimize attack surfaces, and ensure compliance with data protection standards.
Action: Adopt an API lifecycle management framework that tracks each API from inception through deprecation. Automated tools should be used to detect inactive or underused APIs, and policies should require regular review and decommissioning for outdated endpoints.
Eliminating the Risk of Zombie APIs
Zombie APIs are an often-overlooked threat in modern API environments, providing easy access points for attackers due to their outdated protocols, lack of documentation, and unmonitored data flows. As organizations scale their API deployments, the risk of zombie APIs increases, making it essential to adopt proactive management practices.
By enforcing lifecycle management, integrating automated discovery and monitoring tools, and prioritizing compliance and data protection, organizations can minimize the risks posed by zombie APIs. Addressing the “undead” in API environments is critical to maintaining a secure, compliant, and resilient API ecosystem.
In 2025 and beyond, managing zombie APIs will become a standard part of any robust API security strategy. Organizations that fail to address these hidden threats risk falling victim to breaches, data loss, and regulatory violations, jeopardizing both their operations and reputation.
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