7PK - Security Features
In the marshmallow library before 2.15.1 and 3.x before 3.0.0b9 for Python, the schema "only" option treats an empty list as implying no "only" option, which allows a request that was intended to expose no fields to instead expose all fields (if the schema is being filtered dynamically using the "only" option, and there is a user role that produces an empty value for "only").
CWE-254 - Security Features
Security features are integrated into the application infrastructure to protect its resources and the trusted environment against a known exploit, threat, or vulnerability. However, flawed, disabled, or absent security features expose the application to a variety of attacks. This is a multidimensional vulnerability with broad potential impact. It can lead to defacement, confidentiality compromise, system takeover, etc.