CVE-2026-49456: Waku has an Open Redirect via `unstable_redirect` Helper

The unstable_redirect() helper exported from waku/router/server (packages/waku/src/router/define-router.tsx:156–161) accepts an arbitrary string and reflects it unchanged into the HTTP Location response header with no URL validation, scheme restriction, or path-only enforcement. Any application that passes user-controlled input to this helper — the natural pattern documented in the JSDoc and official fixtures — is vulnerable to open redirect attacks. An attacker who convinces a victim to click a crafted link can silently redirect the browser to an arbitrary external domain, enabling phishing, credential harvesting, and OAuth token theft. Additionally, scheme-relative URLs (//evil.example/) bypass naive https?://-only allow-list filters that developers might add as ad-hoc mitigations.

Dynamic PoC confirmed against waku 1.0.0-beta.0 (commit 8e9f542) in an isolated Docker environment. Two independent dynamic runs produced identical results.

Any developer-supplied user input passed to unstable_redirect() is reflected unchanged into the HTTP Location header, enabling navigation to an attacker-controlled domain.