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").
Severity
CVSS 3.0
5.3 medium
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
EPSS
1.9% chance of exploitation in the next 30 days; higher than 79% of CVEs (scores of 2026-10-31)