Highcharts Dashboards / Grid Pro: `DataTable.setCell` and column writers treat `__proto__` as an existing column.

Impact

When a single cell value is written to a data table, the column id is used as a key on the table's column collection without filtering, so a column id of __proto__ resolves to Object.prototype, is taken for an existing column, and the write lands at the row index on Object.prototype; a column id of constructor writes onto the Object constructor in the same way. In Dashboards releases that still supported column aliases, the id is first resolved through the alias map, so a literal __proto__ id is redirected harmlessly there, while an alias whose target is __proto__, which the connector's data table options accept, reaches the same write. An attacker who controls the column id can thereby set integer-keyed properties on Object.prototype, one per row index, holding the written value; named properties cannot be reached through these paths, because the row index is a number. The integer keys still affect every object in the page: reading an out-of-range index on any array or plain object returns the injected value, and for...in over any object yields the injected keys, so unrelated code can take branches it should not using attacker-supplied data, and rendering can fail as a side effect. In Dashboards the write is reached through the Highcharts component's connector write-back, which is enabled by default through allowConnectorUpdate and takes the column id from the component's columnAssignment, or in the earliest releases from the series name, whe…