CVE-2026-118246: Highcharts Core: `breadcrumbs.style` keys become SVG event-handler attributes

The breadcrumbs style option is applied to the breadcrumb button as SVG attributes rather than as CSS, and the attribute names are not filtered. An attacker who controls the chart configuration can supply keys under breadcrumbs.style that name event handlers, and those keys become live handlers on the breadcrumb button, so the attacker’s script runs in the origin of the page hosting the chart. The option is reached through drilldown.breadcrumbs, navigation.breadcrumbs and the breadcrumbs option of the treemap, sunburst and treegraph series. Exploitation requires that untrusted data reach the chart configuration and that a user drill down, or traverse into a level of a hierarchical series, so that the breadcrumbs render, and then hover over or activate the breadcrumb button. Charts rendered in styled mode do not apply the option and are not affected. Charts built with Highcharts Stock, Maps and Gantt are included, since those ship from the same package as Core.