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

Moderate severity GitHub Reviewed Published Jul 8, 2026 in novuhq/novu • Updated Sep 22, 2026

Package

npm @novu/js (npm)

Affected versions

<= 3.17.0

Patched versions

3.18.0

Description

Summary

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).

Affected

novuhq/novu self-hosted and cloud, API <= v3.15.0; @novu/js <= 3.15.0 and @novu/react (Inbox component). Confirmed live-exploitable on v3.15.0 (Docker community compose, default config, default roles).
Condition: an in-app (Inbox) channel is in use, the standard product configuration.
Recipient must use a Chromium-based browser (Chrome, Edge); the javascript: execution does not occur where the browser blocks javascript: in window.open.

Root cause

packages/js/src/ui/context/InboxContext.tsx:108: window.open(url, target ?? DEFAULT_TARGET, DEFAULT_REFERRER) is reached for any URL not starting with /, with no scheme allowlist, so javascript: is passed through.
packages/js/src/ui/components/Notification/DefaultNotification.tsx:103: the notification click handler calls navigate(redirect.url, redirect.target), feeding the stored values into the sink.
apps/api/src/app/inbox/utils/notification-mapper.ts:85-89: maps cta.data.url and cta.data.target into redirect with no validation of either field.
libs/dal/src/repositories/message-template/message-template.schema.ts:41: data: Schema.Types.Mixed accepts the arbitrary target key (not present in the typed interface).
libs/application-generic/src/usecases/compile-in-app-template/compile-in-app-template.usecase.ts:35-36: the v1 render path handlebars-compiles cta.data.url and performs no scheme check.
libs/application-generic/src/schemas/control/in-app-control.schema.ts:24-27: the v2 control schema enforces url: z.string().regex(redirectUrlRegex) which rejects javascript:, the guard absent from the v1 path and the renderer.

Reproduction

novuhq/novu v3.15.0 Docker community compose, default config. Attacker holds an environment API key (or a member session); victim opens the inbox in Chromium.

  1. Create a v1 in-app workflow with a redirect CTA carrying a javascript: URL and target=_self:
POST /v1/workflows   Authorization: ApiKey <key>
{"name":"poc","notificationGroupId":"<ng>","active":true,
 "steps":[{"template":{"type":"in_app","content":"click me",
   "cta":{"type":"redirect","data":{
     "url":"javascript:window.top.__X=document.domain;void 0","target":"_self"}}}}]}
  1. Trigger it to a subscriber, then read the feed with a subscriber token minted from the public application identifier (no secret):
POST /v1/inbox/session {"applicationIdentifier":"<appId>","subscriberId":"<sub>"}
GET  /v1/inbox/notifications   Authorization: Bearer <subscriber-jwt>
-> redirect: {"url":"javascript:window.top.__X=document.domain;void 0","target":"_self"}
  1. The subscriber clicks the notification in the @novu/js / @novu/react Inbox.

Live-verified: the stored javascript: URL is returned verbatim by the inbox feed, and the exact shipped navigate() logic invoked from a real click runs window.open(url,"_self",...), executing the payload in the http://<dashboard>:4000 origin (no CSP); window.top.__X was set to the page origin. On the self-hosted dashboard the test inbox bell uses subscriberId = user.externalId (apps/dashboard/src/components/inbox-button.tsx:102), so a member targets another member's id and the executing payload reads localStorage['self-hosted-jwt'] (apps/dashboard/src/utils/self-hosted/jwt-manager.tsx:4), the dashboard session token.

Impact

  • Stored XSS in the recipient's browser, cross-principal (content author to end-user subscriber), persistent, replicated to every recipient of the workflow.
  • On the self-hosted dashboard origin (no CSP), theft of localStorage['self-hosted-jwt'] yields takeover of another member or admin account.
  • In a customer application embedding the inbox, session and token theft and authenticated actions in that origin.
  • Triggered by the lowest privilege that can author a workflow, default config, one recipient click.

Credit

Jan Kahmen, turingpoint (jan@turingpoint.de)

References

@scopsy scopsy published to novuhq/novu Jul 8, 2026
Published by the National Vulnerability Database Sep 22, 2026
Published to the GitHub Advisory Database Sep 22, 2026
Reviewed Sep 22, 2026
Last updated Sep 22, 2026

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required Low
User interaction Passive
Vulnerable System Impact Metrics
Confidentiality None
Integrity None
Availability None
Subsequent System Impact Metrics
Confidentiality Low
Integrity Low
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N

EPSS score

Weaknesses

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Learn more on MITRE.

CVE ID

CVE-2026-75510

GHSA ID

GHSA-8gr3-5j6f-25gp

Source code

Credits

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