API Security Testing for GDPR Readiness

Client:

BookingSync — a French platform for short-term rental property management

Industry:

Software Development

Focus:

Protecting personal data of users interacting via web portal and API

Main challenge:

Assessing the security of API endpoints to prevent data leaks and unauthorized access

Market:

International (primarily Europe)

Services provided:

Gray-box API penetration testing

Key Takeaways

Assessed API data flows to ensure GDPR compliance

Delivered actionable fixes to improve PII protection

Identified several low-level vulnerabilities

Delivered a report with security enhancement recommendations

100%

compliance with API security best practices

low-level vulnerabilities identified and mitigated

weeks total duration of the testing process

Mar 28, 2025

14 min

Is API expansion always safe for a platform? The international company BookingSync decided not to take any chances and initiated an audit of its API endpoints. The Datami team performed a gray-box pentest and uncovered low-level vulnerabilities. The resulting recommendations helped BookingSync boost its API protection and reduce the risk of data leaks.

BookingSync is a French technology company that provides a platform for managing short-term rental properties. Serving an international market—primarily across Europe—BookingSync enables thousands of hosts and guests to access its services daily through a user-friendly web portal and API integrations.

While the company does not operate in a regulated industry, it handles large volumes of user personal data, making robust system security a top priority.

Objectives and challenges

BookingSync's primary concerns were unauthorized access to its API and potential data leaks. To proactively mitigate reputational risks, the company initiated a scheduled security assessment.

Project objective was to identify potential vulnerabilities in API endpoints and assess their resilience against external threats.

1. Conduct a gray-box pentest of the current API endpoints.
2. Detect vulnerabilities that could lead to data compromise and evaluate the overall security posture.
3. Deliver a comprehensive report with actionable recommendations for improving API documentation and planning future security testing.

Penetration testing

Gray-box pentest of API endpoints

Vulnerability identification

Discovery and prioritization of security risks

Reporting & recommendations

Detailed report with practical advice for improving security

Datami Methodology: Security Testing for BookingSync

Our approach

To assess the security of BookingSync’s API endpoints, Datami employed a gray-box penetration testing approach. The team had partial access to technical documentation, enabling a deeper analysis of endpoint logic and common access scenarios.

We combined automated scans using Burp Suite API Scan with manual testing methods to ensure thorough coverage of both standard and unconventional attack vectors.

Gray-box

The assessment was performed with limited internal knowledge, simulating the actions of a potential attacker with basic access and insight. This approach provided a realistic view of actual risk exposure.

Key stages and solutions

The Datami team conducted a focused security assessment of BookingSync’s API, targeting vulnerabilities that could potentially lead to personal data exposure. A hybrid approach was used, combining automated scanning via Burp Suite API Scan with manual analysis.

The process included the following key stages:

Preparation

Review of technical documentation, test planning, and selection of relevant API endpoints.
Testing

Gray-box pentest using both automated and manual methods, with a focus on authentication mechanisms and resistance to unauthorized access.
Analysis & Reporting

Compilation of a detailed report outlining identified low-level vulnerabilities, along with practical recommendations to improve API security and documentation quality.

Fewer critical risks — more confidence

Results and recommendations

At the start of the project, BookingSync faced an undefined risk level: the platform had been continuously expanding its API endpoints without a full security audit, posing potential threats to the integrity of users’ personal data.

During the gray-box penetration testing, the Datami team identified several low-level vulnerabilities. While not critical, these weaknesses could potentially be exploited to gain unauthorized access.

Datami provided BookingSync with the following recommendations:

Regularly assess new API endpoints for compliance with security standards.
Improve the structure and clarity of API documentation.
Implement an internal process for continuous API testing prior to releases.

Following the implementation of the recommendations, the platform’s security posture improved, and the risk of API-related compromise was significantly reduced. The company avoided a potential data breach that could have led to reputational damage.

The project was completed in just 3 weeks — nearly twice as fast as the typical market timeframe of 4–6 weeks. No critical incidents were detected, and all identified vulnerabilities were promptly addressed.

Key project takeaways

Thanks to Datami's testing, BookingSync gained a current and detailed view of its API security status, mitigated low-level risks, and developed a clear action plan for future improvements.

The project helped strengthen the protection of users’ personal data and prevent potential breaches.

This case study confirms that even advanced tech companies with mature digital products require regular penetration testing to maintain a strong security posture.

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