Epoch AI Demonstrates GLM 5.3 Can Build Full Firefox Exploit Chains Within 48 Hours

Researchers at Epoch AI showed that the open‑weight language model GLM 5.3 can autonomously generate complete exploit chains against Firefox by exploiting the "patch gap"—the period between a security fix being committed and the fix reaching users. Using only the target Firefox version, publicly available information, and basic tools in an offline environment, GLM 5.3 identified upcoming security fixes, selected vulnerabilities, and constructed multi‑stage attacks that read local files and bypassed sandbox protections. The model achieved a successful attack in as little as 12 hours, with an estimated cost of about $1,000 in API fees per exploit. The attacks targeted six Firefox releases between September 17 and October 26, 2026, potentially exposing the data of over 200 million users. Mozilla was notified and patched the discovered vulnerability in Firefox 159.0, released on October 27, 2026.