A web developer has implemented HTML5 optimizations into a legacy web application. One of the modifications the web developer made was the following client side optimization…

Switching to sessionStorage would cause the copied cookie data to expire when the browser tab closes, but the session cookie value is still readable by JavaScript during the session and remains fully vulnerable to XSS-based exfiltration within that window.

Marking cookies HttpOnly and Secure are valuable hardening measures - HttpOnly prevents JavaScript from reading the cookie via document.cookie and Secure restricts transmission to HTTPS - but neither attribute directly addresses the scoping problem of which cookies are exposed to the current page context and stored in localStorage.

The Domain and Path attributes on the Set-Cookie header control which cookies the browser makes visible to a given page through document.cookie - by scoping cookies tightly to only the relevant domain and path, the developer ensures that the minimum necessary cookies are readable by JavaScript, directly limiting what sensitive data ends up persisted in localStorage and reducing the cross-context exposure risk.

Migrating to server-side session mechanisms is a comprehensive architectural change that would eliminate client-side cookie exposure entirely, but the recommendation requested here is scoped to the specific client-side optimization already implemented, not a full re-architecture of the session model.