GLM-5.3 chained a public Firefox patch clue with a sandbox bypass in a test lab

Epoch researchers gave an open-weight model exploit-development infrastructure and public information about a renderer flaw while browser users still faced an update gap. In six tested Firefox builds, GLM-5.3 helped construct chains that coupled the renderer weakness with a previously unknown filesystem protection bypass. The second weakness was later patched in Firefox 159.0. A chain that reaches a local file is more consequential than a renderer crash, but it still requires the attacker to deliver content into a vulnerable browser and control the full chain.

The paper separates an expensive initial research setup from lower marginal reruns. Its roughly 1,000 dollar per-version figure does not cover a reported six-figure setup investment, and the researchers did not obtain a comparable Chrome success after substantial effort. These negative and cost results matter when describing autonomous offensive capability; one model success cannot be projected into a universal browser exploit service.