CVE-2026-118249: Highcharts: series column construction writes to Object.prototype

When series columns are built from point objects, the point option keys are used directly as data column ids, so the write that populates a column reaches Object.prototype and the Object constructor. Keys named __proto__ and constructor survive JSON.parse as own enumerable properties, so an attacker who controls the point objects can set integer-keyed properties on Object.prototype, one per point index, to values of their choosing. Named properties cannot be reached this way. The integer keys still affect every object in the page: reading an out-of-range index on any array or plain object returns the attacker’s 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. The properties remain in place once the chart has been built, and no user interaction is required beyond rendering the chart.

Consequences beyond disruption depend on the consuming application.