CVE-2026-59896: hono/jsx does not isolate context per request, leading to cross-request data disclosure

Summary

hono/jsx did not isolate context values per request during server-side rendering. While an async component was suspended on await, its provided context value stayed observable to other requests rendering concurrently, so useContext() could return a value from a different in-flight request.

Details

During server-side rendering, context values were kept in a process-wide structure rather than scoped to each request's render. While an async component awaited, another request entering the same provider could observe or replace the value; when the first render resumed, it could read the other request's context.

This affects the usual ways request-scoped data is passed through a server-rendered JSX tree:

- createContext() / useContext() - the jsxRenderer middleware and useRequestContext()

It arises only when context is read after an await inside an async component while requests render concurrently. Reading context synchronously (before any await), purely synchronous rendering, and client-side (DOM) rendering are not affected.

Impact

Under concurrent requests, a response could be rendered with another request's context. A user may receive HTML rendered for a different user, and an authorization check performed after an await may be evaluated against another user's data.

This may lead to:

- disclosure of rendered output intended for another user - authorization decisions made with the wrong request's context - cross-request mixing of session or other request-scoped state