Full Report
That’s a lot. No, it’s an extraordinary number: Since February, the Firefox team has been working around the clock using frontier AI models to find and fix latent security vulnerabilities in the browser. We wrote previously about our collaboration with Anthropic to scan Firefox with Opus 4.6, which led to fixes for 22 security-sensitive bugs in Firefox 148. As part of our continued collaboration with Anthropic, we had the opportunity to apply an early version of Claude Mythos Preview to Firefox. This week’s release of Firefox 150 includes fixes for 271 vulnerabilities identified during this initial evaluation...
Analysis Summary
# Vulnerability: Massive AI-Driven Discovery of 271 Latent Flaws in Firefox
## CVE Details
- **CVE ID:** Not specified individually in the summary (271 unique vulnerabilities addressed)
- **CVSS Score:** Varies (Ranging from Low to High/Critical; characterized as "security-sensitive")
- **CWE:** Diverse; likely includes Memory Safety (CWE-119), Use-After-Free (CWE-416), and Logic Errors given the nature of browser hardening.
## Affected Systems
- **Products:** Mozilla Firefox
- **Versions:** All versions prior to Firefox 150
- **Configurations:** Default browser configurations
## Vulnerability Description
These vulnerabilities represent a massive collection of "latent" security flaws—bugs that existed in the codebase but had remained undetected by traditional Fuzzing, Static Analysis (SAST), and manual code review. The flaws were identified using **Claude Mythos Preview**, an advanced frontier AI model by Anthropic, which was applied to the Firefox source code. While specific technical details for all 271 bugs are not itemized, they are described as "security-sensitive," typically involving memory corruption or sandbox escapes common in complex C++ browser engines.
## Exploitation
- **Status:** Not exploited (Identified internally via AI-driven research before discovery by malicious actors)
- **Complexity:** Varies
- **Attack Vector:** Network (Remote execution via malicious web content)
## Impact
- **Confidentiality:** High (Potential for data exfiltration)
- **Integrity:** High (Potential for unauthorized code execution)
- **Availability:** High (Potential for browser crashes or denial of service)
## Remediation
### Patches
- **Firefox 150:** Users must update to version 150 or later to remediate the 271 identified vulnerabilities.
- **Firefox 148:** Previously addressed 22 bugs found via earlier Anthropic models (Opus 4.6).
### Workarounds
- No specific workarounds are provided; immediate update to Firefox 150 is the only recommended mitigation.
## Detection
- **Indicators of compromise:** None currently identified (these were discovered proactively).
- **Detection methods and tools:** Mozilla recommends that organizations use the same frontier AI models (like Claude Mythos) for defensive scanning of proprietary codebases to identify similar high-volume latent flaws.
## References
- **Vendor Advisories:** Mozilla Security Blog [hxxps://blog.mozilla.org/en/firefox/ai-security-zero-day-vulnerabilities/]
- **News Coverage:** Ars Technica [hxxps://arstechnica.com/ai/2026/04/mozilla-anthropics-mythos-found-271-zero-day-vulnerabilities-in-firefox-150/]
- **Expert Analysis:** Schneier on Security [hxxps://www.schneier.com/blog/archives/2026/04/claude-mythos-has-found-271-zero-days-in-firefox.html]