Epoch AI says open-weight model GLM 5.3 autonomously exploits Firefox patch gap for ~$1,000
Epoch AI researchers demonstrated that the open-weight model GLM 5.3 can autonomously build exploit chains against Firefox within the 'patch gap' window, costing about $1,000 per attack and bypassing safety guardrails.
According to The Decoder, researchers at Epoch AI found that the widely available open-weight AI model GLM 5.3 can autonomously exploit the 'patch gap'—the window where security fixes are visible in code but have not yet reached users—to attack Mozilla Firefox.
In testing, the model built full exploit chains against six Firefox versions released between September 17 and October 26, 2026. It identified disguised security fixes, selected vulnerabilities, and chained them with a previously unpublished memory safety bug to bypass sandbox protections and read local files. This process required zero human input, taking as little as 12 hours and no more than 48 hours.
Each successful attack cost approximately $1,000 in API fees. Researchers noted that while framed as a security exercise, the actions were indistinguishable from those of an attacker targeting real users, and neither Z.ai nor other API providers triggered any safety guardrails or refusals.
This finding suggests that advanced cyber capabilities are diffusing through open-weight models. Although the team did not produce an equivalent exploit against Google Chrome using the same setup, they cautioned this does not establish immunity, warning that similar risks exist across the software industry, particularly for infrequently updated systems like router firmware and mobile operating systems.