CVE-2026-49455

Summary Waku's RSC request dispatcher invokes server actions without validating the request's Origin (or Sec-Fetch-Site) header. A cross-origin web attacker can therefore cause a victim browser to issue an authenticated POST to a registered server action endpoint using a CORS-safelisted content type (text/plain), which does not trigger a preflight. Any state-mutating server action that the application exposes via 'use server' can be invoked with the victim's cookies attached. A working proof-of-concept demonstrates the vulnerability against waku 1.0.0-beta.0 dev server: a cross-origin POST with Content-Type: text/plain invokes a registered 'use server' action and returns HTTP 200 with an RSC stream response. The same defect affects the progressive-enhancement (no-JavaScript) server action path: a cross-origin HTML form auto-submitting multipart/form-data reaches the dispatch through a second unguarded branch of the request handler, dynamically confirmed on 2026-05-17. Both branches were confirmed exploitable from opaque-origin contexts (sandboxed iframes, file:// navigation, browser extension pages), which send Origin: null — a value no Origin guard exists to reject. This is the same vulnerability class previously disclosed for Next.js Server Actions (GHSA-mq59-m269-xvcx); waku's implementation is broader in that no Origin check exists at all in the default request handler. Root cause In packages/waku/src/lib/utils/request.ts: // line 29 if (pathname.startsWith(rscPathPrefix)) { rscPath = decodeRscPath(pathname.slice(rscPathPrefix.length)); const actionId = decodeFuncId(rscPath); if (actionId) { const body = await getActionBody(req); const args = await decodeReply(body, { temporaryReferences }); const action = await loadServerAction(actionId); // ...action is invoked with attacker-supplied args } } The sibling else if (req.method === 'POST') branch (line 61) does enforce a method check, but only for non-RSC paths. The RSC dispatch branch has no equivalent guard

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