undici: redirect cache flaw lets attackers poison or read cached responses

undici is an HTTP client for Node.js. In versions 7.30.1 and 8.12.2 through 8.12.3, when an originless Agent composes the redirect and shared cache interceptors, undici decides whether to store the final response under the original request key by inspecting only the final redirect hop, which bypasses the earlier fix for CVE-2026-109829 that compared only the initial and final origins. A redirect that bounces through an untrusted origin and returns to the trusted origin is still cached under the trusted key, an intermediate hop's Vary is dropped so a response that varies on Authorization or Cookie can be served to a different user, and an intermediate hop's no-cache or default-uncacheable status is ignored so a non-storable redirect is laundered into a cacheable entry. An attacker who controls a redirect target from a trusted URL can poison the cached entry for that URL or have a private, per-user response served to a later caller. The issue is fixed in undici 7.30.2 and 8.12.4, and users should upgrade to one of those versions or later. As a workaround, compose the interceptors as cache then redirect, use per-origin dispatchers and cache stores, or disable shared caching on redirect-capable requests.