Epoch AI Reports Open-Weight GLM 5.3 Exploits Firefox Patch Gap

Epoch AI demonstrated that GLM 5.3, an open-weight model from Z.ai, autonomously exploited a vulnerability in six recent Firefox versions before patches were applied, at a low cost per version. The exploit allowed reading local files via crafted webpages, risking user data for over 200 million Firefox users. Mozilla patched the vulnerability in Firefox 159.0 on October 27, 2026, following Epoch's disclosure.