Xbow's AI agents vs V8: bounds confusion, GC tricks and TOCTOU details revealed in Q&A
Xbow · x · 2026-10-14
Security researcher Brendan Dolan-Gavitt (moyix) answers detailed technical questions about how Xbow's AI agents autonomously discovered V8 sandbox escape bugs, covering two stages:
- Stage 1 (Maglev/deopt): why Array.prototype.at() was chosen as the bounds-confusion primitive over more common vectors like Array.prototype.fill or typed-array accesses, and how the large-object-space trick for recovering stable addresses held up across GC timing.
- Stage 2 (WebP/TOCTOU): how the agents discovered the detach-notification chain could be surgically edited via in-cage writes.
The thread gives a rare look at the concrete engineering inside agent-driven browser vulnerability research.
Related event: moyix Details How XBow's AI Agent Autonomously Developed V8 Sandbox Escape(7 posts)→
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