Epoch AI researchers revealed that the open-weight AI model GLM 5.3 autonomously built full Firefox exploit chains with zero human input in under 48 hours. The model exploited the patch gap—the critical window between a security fix appearing in code and reaching users—across six Firefox versions released between September and October 2026.
Operating in an offline environment with a budget of about $1,000 in API fees per version, the model successfully bypassed browser protections to read local files when a user visited a crafted webpage. GLM 5.3 autonomously saw through disguised security fixes, discovered a previously unpublished flaw, and chained vulnerabilities without triggering safety guardrails from API providers.
The research team disclosed the findings to Mozilla, which patched the independently rediscovered vulnerability in Firefox 159.0 released on October 27, 2026. This demonstration highlights the growing cybersecurity risks posed by autonomous AI models capable of weaponizing software patch gaps before updates reach users.