Waku has an Open Redirect via unstable_redirect Helper
Summary
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.
Root Cause
packages/waku/src/router/define-router.tsx:156–161:
export function unstable_redirect(
location: string, // only URL pathname is supported.
status: 303 | 307 | 308 = 307,
): never {
throw createCustomError('Redirect', { status, location });
}The JSDoc comment states "only URL pathname is supported", but this constraint is expressed as documentation only — the function performs no validation. The location value propagates via createCustomError (custom-errors.ts:22–26) into an error digest, is recovered by getErrorInfo in the request handler (handler.ts:79–89), and reflected directly into headers.location of the outgoing Response with no sanitization:
if (info?.location) {
headers.location = info.location; // handler.ts:87 — unvalidated reflection
}
return new Response(body, { status, headers });Trigger (one-line summary)
Any developer-supplied user input passed to unstable_redirect() is reflected unchanged into the HTTP Location header, enabling navigation to an attacker-controlled domain.
Affected Entry Surfaces
unstable_redirect(location, status?)—waku/router/serverpublic export- Any page/route component that passes
searchParams,query, or other user-
unstable_redirect (the standard post-login or callback
redirect pattern)
- All waku adapters (Node.js, Cloudflare Workers, Vercel Edge, Deno) share the same
handler.ts reflection path; cross-runtime CRLF parity is unaudited (see note
below)Additional Defense-in-Depth Concern
On Node.js, CRLF injection via the Location header is rejected by node:_http_outgoing.setHeader (ERR_INVALID_CHAR). This defense is platform-specific and not present in the waku source. Cloudflare Workers, Deno Deploy, and other edge runtimes have not been verified to offer equivalent protection. A cross-runtime audit is recommended.
Suggested Fix Outline
Validate the location argument inside unstable_redirect before the error is thrown: reject any value that does not begin with a single / (no //), and reject any value containing control characters (\x00–\x1f). An opt-in allow-list for intentional cross-origin redirects can be provided via a framework configuration option.
Disclosure
| Field | Value |
|------------------|------------------------------------|
| Reporter | j0hndo ([email protected]) |
| Discovery date | 2026-05-17 |
| Embargo | 90 days from acknowledgment |
| Patched version | Not yet available |
| Public references| CWE-601; OWASP A01:2021 |