INSERT ... ON CONFLICT DO UPDATE commands in PostgreSQL 10.x before 10.1,
9.6.x before 9.6.6, and 9.5.x before 9.5.10 disclose table contents that
the invoker lacks privilege to read. These exploits affect only tables
where the attacker lacks full read access but has both INSERT and UPDATE
privileges. Exploits bypass row level security policies and lack of SELECT
privilege.

sbeattie

RLS and ON CONFLICT DO UPDATE introduced in 9.5