Anthropic’s cutting-edge AI model, Claude Mythos Preview, has identified an unprecedented 271 zero-day vulnerabilities within Mozilla Firefox, marking a significant advancement in AI-driven cybersecurity. These vulnerabilities have been addressed in the latest Firefox 150 release, representing the most substantial single batch of security fixes in the browser’s history.
The collaboration between Mozilla and Anthropic began in February 2026, aiming to enhance Firefox’s security through advanced AI analysis. Initially, the partnership utilized Claude Opus 4.6, which, over a two-week period, uncovered 22 vulnerabilities—14 of which were classified as high-severity. These findings were promptly addressed in Firefox 148, demonstrating the potential of AI to identify critical security issues more rapidly than traditional human-led efforts.
Building upon this success, Mozilla integrated an early version of Claude Mythos Preview into their codebase analysis. The results were remarkable: 271 vulnerabilities were identified in a single evaluation, all of which have been patched in the recent Firefox 150 release. To put this into perspective, throughout 2025, Mozilla addressed approximately 73 high-severity vulnerabilities in Firefox. The AI-driven discovery in this instance is nearly four times that annual figure, achieved in a single sweep.
Claude Mythos stands out due to its autonomous capability to detect and exploit zero-day vulnerabilities across various operating systems and browsers without human intervention beyond the initial prompt. Benchmark tests have showcased its exceptional performance, achieving 93.9% on SWE-bench and 97.6% on USAMO. Specifically, within Firefox’s JavaScript shell, Mythos successfully exploited 72.4% of identified vulnerabilities and achieved register control in an additional 11.6% of cases.
The implications of this development are profound for the cybersecurity industry. Historically, attackers have had the advantage, needing to find only a single flaw, while defenders were tasked with protecting vast and complex systems. AI tools like Mythos are now leveling the playing field by enabling defenders to systematically and efficiently discover vulnerabilities.
Beyond Firefox, Mythos has uncovered longstanding vulnerabilities in other critical infrastructures, including a 27-year-old bug in OpenBSD, a 16-year-old flaw in FFmpeg, and a 17-year-old vulnerability in FreeBSD. These discoveries underscore AI’s potential to identify latent risks that have eluded decades of human and automated analysis.
Mozilla engineers have expressed optimism about this collaboration, noting that while the work is ongoing, the partnership has reached a pivotal point. As AI-powered vulnerability research becomes more accessible to defenders, the longstanding belief that achieving zero exploits is unattainable may soon be challenged.
In conclusion, the integration of advanced AI models like Claude Mythos into cybersecurity practices represents a transformative shift. By harnessing AI’s capabilities, organizations can proactively identify and address vulnerabilities, enhancing the security and resilience of digital infrastructures.
Anthropic’s Claude Mythos AI uncovers 271 zero-day vulnerabilities in Firefox, leading to the most significant security update in the browser’s history. #CyberSecurity #AI #MozillaFirefox
Claude Mythos AI zero-day vulnerabilities in Firefox
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Category: Security News
