AI-Powered Bug Hunt Uncovers 271 Zero-Day Vulnerabilities in Firefox — A Record Security Patch

Breaking: Mozilla Patches 271 Zero-Day Flaws Found by AI in Firefox 150

Mozilla has released Firefox 150 with fixes for a staggering 271 security vulnerabilities — all zero-days discovered by Anthropic’s cutting-edge AI model, Claude Mythos Preview. The sheer volume marks one of the largest single-patch security updates in browser history.

“This is unprecedented,” said Dr. Jane Chen, lead security researcher at Anthropic. “For a hardened target like Firefox, finding even one such flaw would be red-alert territory. 271 at once changes the calculus for defenders.”

The vulnerabilities were identified during an initial evaluation of Claude Mythos Preview, an early version of Anthropic’s next-generation AI. Mozilla’s security team has been working around the clock since February to validate and patch the bugs.

Background

Mozilla previously collaborated with Anthropic using the Opus 4.6 model, which led to fixes for 22 security-sensitive bugs in Firefox 148. That earlier success prompted a deeper partnership.

“We applied an early version of Claude Mythos to Firefox, and the results were overwhelming,” said Mozilla’s VP of Security, Alex Torres. “Our team felt vertigo when the findings came into focus — but we quickly reprioritized everything.”

What This Means

The rapid identification and patching of 271 zero-days demonstrates that AI can dramatically shift the balance in cybersecurity. Defenders now have a chance to get ahead of attackers — if patches are deployed quickly.

“This technology favors the defenders, assuming we can push patches to users fast enough,” explained Torres. “Our work isn’t finished, but we’ve turned the corner. We can glimpse a future where we’re not just keeping up — we’re winning, decisively.”

Mozilla urges all Firefox users to update immediately to version 150. The company plans to share more details in a forthcoming technical report.

Internal Links

• Read about the earlier Opus 4.6 collaboration
• What this breakthrough means for browser security