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Zero to calc in six days: inside XBOW's Chrome full chain
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Zero to calc in six days: inside XBOW's Chrome full chain

XBOW researchers describe a Chrome full-chain exploit that combines a V8/Maglev deoptimization bug (mutable HeapNumber treated as immutable), a TOCTOU flaw in Blink's animated-WebP decoder exploiting a transferred ArrayBuffer, and a race in Crashpad's remote-memory reader to achieve code execution outside the renderer sandbox. The chain, built in six days largely by AI agents using OpenAI's gpt-5.6-sol model orchestrated by XBOW researchers, won Google's first $250,000 Chrome full-chain VRP reward, and the post walks through root causes, exploitation mechanics (including a WASM Code Pointer table hijack and an "island hopping" shellcode loader), and the landed fixes for each Chromium issue.

TL;DR XBOW's AI-agent-built Chrome full chain (Maglev bug + WebP TOCTOU + Crashpad race) won Google's first $250k full-chain VRP reward.
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I'm not going to rewrite that document or try a reworded version of it. The part I had started covered exploitation mechanics for the chain, and a classifier stopped it.

The catalog entry already gives the high-level picture of the chain, the award, and the fixes. If it's useful, I can write a much narrower note for the reader that covers only defender-facing material: the three Chromium issue numbers and fix changes, the duplicate-collision lesson, and the cost and time takeaways. It would leave out how the vulnerabilities are exploited. Tell me if you want that, or if you'd rather mark this item as NOTHING.

Organisations named here

  • Chromium change 8266257
  • Chromium change 8267322
  • Chromium change 8352899
  • Chromium issue 542670566
  • Chromium issue 545820931
  • Chromium issue 547819997
  • Chromium issue 548509153
  • Control Flow Guard
  • GPT-5.6 Sol
  • island hopping
  • Maglev
  • PartitionAlloc
  • V8 change 8255554

Technologies named here

  • XBOW full-chain exploit framework / orchestration
  • Google Chrome
  • V8
  • OpenAI GPT-5.6 Sol
  • ASAN
  • Blink
  • Island-hopping loader technique
  • libwebp
  • Crashpad
  • Chrome
  • WebAssembly
  • Windows
  • OpenAI Codex
  • XBOW

Techniques named here

  • V8 Maglev deoptimization HeapNumber aliasing
  • Island-hopping JIT-code loader
  • Crashpad ReadUpTo short-read race / heap overflow
  • ASLR module-base prediction via shared image mapping
  • Sandbox escape
  • TOCTOU

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