Researchers at Epoch AI tested the GLM 5.3 model by providing it with browser version details and access to public code changes. The AI autonomously identified security patches, selected vulnerabilities, and constructed exploit chains to bypass sandbox protections and read local files.
The attack was successful against six Firefox releases issued between September 17 and October 26, 2026. The model required between 12 and 48 hours to develop each exploit. Mozilla patched the vulnerability in Firefox 159.0, released on October 27, following notification from the researchers.
Attempts to replicate the attack on Chrome were unsuccessful, despite an investment of $100 000. Epoch AI notes that the 'patch gap' remains a universal risk, as public repositories allow attackers to create exploits before updates reach users. The organization warns that open-weight models lower the barrier for such cyberattacks.
