The vulnerability stems from improper handling of parameter arrays containing nil values and empty hashes in query construction. The primary vulnerable function is ActiveRecord::QueryMethods#where which processes WHERE clause conditions. The patch modifies this method to add safeguards against empty hashes and [nil] values. Dynamic finders (find_by_*) that rely on where() inherit this vulnerability. The evidence comes from the security advisory's description of NULL check bypass and the nature of fixes shown in referenced patches that modify query generation logic.