Mozilla Patches 271 Firefox Vulnerabilities Identified by Anthropic’s Claude Mythos
April 22, 2026 – 6:35 pm
Summary:
Mozilla released Firefox 150 with fixes for 271 security vulnerabilities identified by Anthropic’s Claude Mythos Preview, an unreleased frontier AI model distributed under the restricted Project Glasswing program. This collaboration began earlier this year when Claude Opus 4.6 found 22 bugs in Firefox 148. Mythos discovered over twelve times as many vulnerabilities.
The Zero-Days Are Numbered
Mozilla emphasizes that:
“We haven’t seen any bugs that couldn’t have been found by an elite human researcher.”
The remarkable aspect is not the exotic nature of the vulnerabilities but the speed at which they were discovered.
What is Claude Mythos?
Claude Mythos Preview is a general-purpose frontier AI model part of Anthropic’s Project Glasswing. Evaluated by the UK AI Security Institute, Mythos can:
- Execute multi-stage network attacks autonomously.
- Chain multiple small vulnerabilities into powerful attacks.
- Reconstruct source code to find exploitable weaknesses.
- Build custom tools for lateral movement and data extraction once inside a network.
Access to Mythos is restricted to 12 named launch partners, including Amazon Web Services.