Enhancing REST API Fuzzing with Access Policy Violation Checks and Injection Attacks

2026-04-01

AI Summary

This work addresses the limitations of existing REST API fuzzing approaches, which primarily focus on crash detection and struggle to effectively uncover access control violations and injection vulnerabilities. To overcome this, the authors propose an enhanced methodology that integrates a novel automated oracle into the security testing phase following fuzzing. This oracle enables precise detection of security issues such as privilege escalation, SQL injection, and cross-site scripting (XSS), while automatically generating executable, multi-language reproduction test cases. Built as an extension of the EvoMaster fuzzer, the approach synergistically combines black-box and white-box strategies and seamlessly integrates into existing fuzzing pipelines. Empirical evaluation across 52 APIs—including both real-world and synthetic systems—demonstrates that the proposed technique significantly improves the detection capability for critical API security vulnerabilities.

Abstract

Due to their widespread use in industry, several techniques have been proposed in the literature to fuzz REST APIs. Existing fuzzers for REST APIs have been focusing on detecting crashes (e.g., 500 HTTP server error status code). However, security vulnerabilities can have major drastic consequences on existing cloud infrastructures. In this paper, we propose a series of novel automated oracles aimed at detecting violations of access policies in REST APIs, as well as executing traditional attacks such as SQL Injection and XSS. These novel automated oracles can be integrated into existing fuzzers, in which, once the fuzzing session is completed, a ``security testing'' phase is executed to verify these oracles. When a security fault is detected, as output our technique is able to general executable test cases in different formats, like Java, Kotlin, Python and JavaScript test suites. Our novel techniques are integrated as an extension of EvoMaster, a state-of-the-art open-source fuzzer for REST APIs. Experiments are carried out on 9 artificial examples, 8 vulnerable-by-design REST APIs with black-box testing, and 36 REST APIs from the WFD corpus with white-box testing, for a total of 52 distinct APIs. Results show that our novel oracles and their automated integration in a fuzzing process can lead to detect security issues in several of these APIs.

Problem

• REST API
• fuzzing
• access policy violation
• injection attacks
• security vulnerabilities

Innovation

• REST API fuzzing
• access policy violation
• injection attacks
• automated oracles
• security testing