CVE-2026-116303: PostgreSQL foreign key and JSON conversions bypass EXECUTE privilege on cast functions

Missing authorization in PostgreSQL type conversion allows a database user to invoke a cast function despite lacking EXECUTE privilege on that function, via foreign keys, tojson(), and others. A successful attack requires the attacker to search each database for access-restricted cast functions and identify confidentiality impact specific to each function implementation found. There are few or no practical examples of an access-restricted cast function or of a cast function having confidentiality impact. Versions before PostgreSQL 18.7, 17.12, 16.16, 15.20, and 14.25 are affected.