During an assessment, a penetration tester sends the following request: POST /services/v1/users/create HTTP/1.1 Host: target-application.com…

The HTTP request is directed at an API endpoint, as indicated by the URL path /services/v1/users/create. The penetration tester is using a fuzzing technique, denoted by (FUZZ), to systematically inject malformed or unexpected data into the Authorization: Bearer header. This action is a direct attempt to test the API's authentication and authorization mechanisms for vulnerabilities, such as weak token validation, improper error handling, or authentication bypasses. Probing an API's security controls in this manner is a form of security testing that falls under the broad category of API abuse.

A. Directory traversal: This attack involves using path manipulation sequences like ../ to access unauthorized directories, which are not present in the request.
C. Server-side request forgery: This attack tricks the server into making unintended requests to other resources; the provided request does not contain any parameters to initiate such an action.
D. Privilege escalation: This is a potential outcome of a successful exploit, not the specific attack technique being performed in this single request.

1. OWASP API Security Top 10 2023. The scenario aligns with testing for API2:2023 - Broken Authentication. This category describes how attackers try to compromise authentication tokens or exploit implementation flaws in authentication. Fuzzing the Authorization header is a primary method for discovering such vulnerabilities. The document states, "Attackers might try to steal user's tokens (...) or try to guess them (brute-force)." Fuzzing is an automated form of this testing.

2. NIST Special Publication 800-115, "Technical Guide to Information Security Testing and Assessment." Section 4.5.3, "Authentication Verifier," discusses testing authentication mechanisms. The guide outlines techniques such as submitting malformed credentials and tokens to check for vulnerabilities in the authentication process, which is precisely what the fuzzing in the scenario is designed to do against the API.

3. Papadimitriou, P., et al. (2021). "A Fuzzing Framework for Conformance Testing of Rich Web APIs." IEEE Transactions on Reliability, 71(2), 877-895. This peer-reviewed paper discusses the use of fuzzing to test web APIs. Section I, "Introduction," states, "Fuzzing is a popular technique for finding security vulnerabilities by providing invalid, unexpected, or random data as inputs to a computer program." Applying this to an API's Authorization header is a standard approach to finding security flaws. (DOI: https://doi.org/10.1109/TR.2021.3076383)