CVE-2026-75510: Novu: Stored XSS in In-App Inbox via notification redirect.url javascript: scheme

The @novu/js In-App Inbox renderer passes a notification’s redirect.url to window.open() with no URL-scheme validation. The value originates from a notification’s call-to-action and is delivered to the recipient verbatim.

An authenticated organization member (or any holder of the environment API key) creates a v1 in-app workflow whose step CTA stores cta.data = { url: "javascript:<payload>", target: "_self" }. The v1 message-template cta.data field is a Mongoose Mixed type, so the arbitrary target key is accepted and persisted. The server-side inbox mapper copies cta.data.url and cta.data.target into the notification’s redirect object with no scheme check. Novu’s v2 control schema validates redirect URLs against redirectUrlRegex (which rejects javascript:), proving the intended invariant; the v1 path and the client renderer do not enforce it.

When the recipient clicks the notification, the inbox calls window.open(url, "_self", "noopener noreferrer"). In Chromium browsers a javascript: URL opened with target="_self" executes in the current document origin (the default _blank is browser-blocked, so the attacker sets _self).

Result: a low-privilege content author runs arbitrary JavaScript in the browser of every recipient who clicks, in the origin that hosts the inbox (the customer application or the self-hosted Novu dashboard, neither of which sends a CSP).