21.6. Function Security
Functions, triggers and row-level security policies allow users to insert
code into the backend server that other users might execute
unintentionally. Hence, these mechanisms permit users to “Trojan
horse” others with relative ease. The strongest protection is tight
control over who can define objects. Where that is infeasible, write
queries referring only to objects having trusted owners. Remove
search_path the public schema and any other schemas
that permit untrusted users to create objects.
Functions run inside the backend server process with the operating system permissions of the database server daemon. If the programming language used for the function allows unchecked memory accesses, it is possible to change the server's internal data structures. Hence, among many other things, such functions can circumvent any system access controls. Function languages that allow such access are considered “untrusted”, and PostgreSQL allows only superusers to create functions written in those languages.