CVE-2026-53633: Vitest Browser: Exposed Browser Mode API Can Proxy CDP and Overwrite Config Files, Leading to RCE

Vitest Browser Mode exposes a cdp() API that forwards raw Chrome DevTools Protocol (CDP) methods over the Vitest browser WebSocket RPC. CDP is not gated by browser.api.allowWrite, browser.api.allowExec, api.allowWrite, or api.allowExec.

As a result, disabling Browser Mode write and exec operations does not prevent a browser API client from using CDP to perform equivalent actions. In a verified reproduction with allowWrite: false and allowExec: false, CDP Page.setDownloadBehavior set the browser download directory to the project root, and CDP Runtime.evaluate downloaded a controlled vite.config.ts. Vitest reloaded the changed config and executed attacker-controlled Node.js code.

When the Browser Mode API is also exposed to the network, this becomes remotely exploitable because the generated browser runner page exposes the API token, active session id, project name, and project root path needed to connect to the browser WebSocket API and select the target download directory.