Epoch AI: GLM 5.3 autonomously hacked 6 Firefox versions using $1,000 of compute via patch-gap exploits
Epoch AI · rss · 2026-10-30
Epoch AI reports that GLM 5.3, an open-weight model released by Z.ai in August, autonomously exploited the "patch gap" — the window between a security fix being published and shipped to users — to compromise all six Firefox versions released between Sept 17 and Oct 26.
Key findings
- Mimicking a low-resourced attacker with only publicly available info, GLM 5.3 reverse-engineered vulnerabilities from Mozilla's published-but-unshipped fixes and built webpages that could read a visitor's local file with zero further interaction. Each successful attack cost $1,000 in compute; the fastest attempt took just 12 hours (total research spend exceeded $100K in API costs).
- Every exploit chained a patch-gap vulnerability with a separate undisclosed flaw to bypass protections. Mozilla patched that flaw in Firefox 159.0 on Oct 27.
- Attacks on Chrome failed despite $100K spent, but the team says stronger open-weight models like the upcoming Kimi K3.1 Pro could change that.
- No safeguards or refusals were triggered from any provider, including Z.ai.
Recommendations: shrink the patch-gap window by keeping fixes private until deployable, shipping faster, and avoiding batching chainable vulnerability patches.
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