Six days of work and about $40,000 in model tokens were enough for Xbow researchers to cut through Chrome’s layered defenses and land code on Windows machines, a feat Google rated worth its top $250,000 bounty.
The startup’s team, Brendan Dolan-Gavitt, Andres Luksenberg, Baul Lee and Willem Pinckaers, chained three zero-days found during a break at the Black Hat and DEF CON conferences, with OpenAI’s GPT-5.6 Sol model doing much of the searching and proof-of-concept building. Xbow puts the exposed population near one billion users.
Chief executive Oege de Moor said a veteran of a three-letter intelligence agency told him a comparable chain used to take six months of human effort. The humans still steered: they picked targets, fed context, challenged the agents’ findings and chose which pieces to join.
Two walls, three stages
Chrome stacks a V8 sandbox inside an operating system process sandbox. Breaking out of the first does not hand over the machine, because the outer layer still fences the renderer. The Xbow chain crossed both, using three separate bug stages, as Dolan-Gavitt detailed in a technical writeup.
The takeaway for defenders is not that browsers are soft. It is that agent-driven research compresses the time between a code audit starting and an exploit working, so patch windows for browser fleets should be measured in days rather than weeks.
