MariaDB Connector/Node.js: SQL injection through object keys in SET expansion (permitSetMultiParamEntries)

QFinch assessment

With the non-default permitSetMultiParamEntries option enabled, an object passed as a query parameter is expanded into a SET clause, each key becoming a column name. The three code paths implementing that expansion built the backtick-quoted identifier by hand and wrote the key out unescaped, while only the value was escaped.

Potential impact

An application that enables permitSetMultiParamEntries and passes an object with attacker-influenced keys into a statement such as conn.query('UPDATE users SET ? WHERE id = ?', [body, id]) allows the caller to write columns the application never intended to expose — a role, balance or password column — and to append arbitrary SQL to the statement, since the injected text is not confined to an assignment. Exposure requires the option to be enabled: it is off by default, and with it off the object is serialised and escaped as a single string literal, so the key never reaches the SQL grammar. Passing a request body into this API is, however, the ordinary reason to enable the option. An application that enables it is asking for keys to become column names, not for keys to become arbitrary SQL.