AdvisoriesToolsStatsChecklistSubmitGet the email
← All advisories
CVE-2026-120338criticalCode execution2026-11-01

CVE-2026-120338: Prefab UI's Generative UI sandbox runs caller-supplied Python inside Pyodide, Python compiled to WebAssembly, in a Deno subprocess. The feature is documented as

Prefab UI's Generative UI sandbox runs caller-supplied Python inside Pyodide, Python compiled to WebAssembly, in a Deno subprocess. The feature is documented as isolation for untrusted code, including LLM-written UI.

01.

What it is

Prefab UI's Generative UI sandbox runs caller-supplied Python inside Pyodide, Python compiled to WebAssembly, in a Deno subprocess. The feature is documented as isolation for untrusted code, including LLM-written UI. From prefab-ui 0.14.0 through 0.20.2 the launcher starts Deno with unrestricted --allow-read, --allow-write, and --allow-net, and the runner leaves the Deno API on the JavaScript global object. Pyodide's js module proxies that global, so the Python can call Deno.readTextFileSync and Deno.writeTextFileSync.

02.

How to check

  1. Compare your installed version with the range above (command below).
03.

How to fix

    04.

    Sources

    More advisories for this tool
    The weekly email

    One email a week. Only what changed.

    Every new security hole in AI coding tools, MCP servers, app builders and the stacks they generate (Next.js, Supabase, Node, PHP), each with how to check your app and the fix. No roundups of things you already read.

    Free, one email a week. Read the latest issue first if you like. One-click unsubscribe in every email. We never sell or share addresses.