Malvertising
The ad network is the delivery path. A 'legitimate' page, a hostile creative.
Malvertising is spreading malware through online advertising: a hostile ad injected into an otherwise ordinary page or ad network. The site owner may be innocent. Your browser is not a court.
Patch the browser, consider enterprise ad filtering, and do not treat HTTPS plus a known brand as a code-signing ceremony.
Fact source: ASD's ACSC glossary.