js-toml is a TOML parser for JavaScript, Prior to version 1.1.2, the interpreter checks whether a key already exists in a parser-built container with if (object[key]) instead of if (key in object). When the prior value is a falsy primitive — false, 0, 0n, 0.0, -0, or "" — the duplicate-key branch is skipped and the value is silently overwritten by a later sub-table, dotted-key sub-table, or array-of-tables sharing the same name. Per the TOML 1.0.0 spec ("Defining a key multiple times is invalid"; "You cannot define any key or table more than once"), this should be a parse error. The result is structural type confusion of attacker-named keys in the value returned by load(). A boolean-typed false (or numeric 0) becomes a truthy object. Host applications that gate behavior on if…