'Defenders finally have a chance to win, decisively': Firefox CTO raves about Claude Mythos' bug hunting capabilities after it finds 271 vulnerabilities

When you create anything, whether that be software or a short story about two characters that never meet, there's no telling what a fresh pair of eyes will bring to the work. Once a work breaches containment, your adoring audience may reward you with a short work of fanfiction—or make you kick yourself by immediately sniffing out a zero-day exploit. Well, Firefox claims that thanks to AI, 'the zero-days are numbered.'

Firefox teamed up with Anthropic’s Frontier Red Team earlier this year to leverage AI tools in finding and securing zero-day exploits before they have a chance to be unearthed in the real world. As part of that collaboration, Mozilla recently applied an early version of Claude Mythos to the Firefox bug hunt.

The bot found 271 vulnerabilities, which the browser team were then able to fix and ship as part of Firefox 150. Coupled with reports of Claude Mythos finding thousands of vulnerabilities in 'every major operating system and every major web browser, along with a range of other important pieces of software' earlier this month, this could be a security game-changer.

Firefox CTO Bobby Holley is quick to note that none of the bugs found by Claude Mythos "couldn’t have been found by an elite human researcher," but also highlights that much of security is a battle fought "to a draw."

"Vendors of critical internet-exposed software like Firefox take security extremely seriously and have teams of people who get out of bed every morning thinking about how to keep users safe," he explains, "Nevertheless, we’ve all long quietly acknowledged that bringing exploits to zero was an unrealistic goal."

This is largely because it can be so time-consuming for even a team of 'elite human researchers' to pore over source code and look for exploits. Holley reflects on the sense of 'vertigo' these sorts of AI-assisted findings brought up for the browser team, sharing, "Just one such bug would have been red-alert in 2025, and so many at once makes you stop to wonder whether it’s even possible to keep up."

But ultimately, Holley is hopeful for the future of security supported by AI assistance: "Our work isn’t finished, but we’ve turned the corner and can glimpse a future much better than just keeping up. Defenders finally have a chance to win, decisively."

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