How severe is GHSA-26wg-9xf2-q495?

GHSA-26wg-9xf2-q495 has a CVSS score of 8.1/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by GHSA-26wg-9xf2-q495?

GHSA-26wg-9xf2-q495 affects the following packages: novu/api (npm). Ecosystems affected: npm.

How do I fix GHSA-26wg-9xf2-q495?

Update novu/api to 3.15.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-26wg-9xf2-q495 is resolved across your whole dependency graph.

How do I detect GHSA-26wg-9xf2-q495 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for novu/api, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate GHSA-26wg-9xf2-q495 if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is GHSA-26wg-9xf2-q495 actively exploited in the wild?

No public exploit code has been indexed for GHSA-26wg-9xf2-q495 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

When was GHSA-26wg-9xf2-q495 published, and has it been updated?

GHSA-26wg-9xf2-q495 was published on April 14, 2026 and was last updated on April 14, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

HIGH severity

Novu has a XSS sanitization bypassGHSA-26wg-9xf2-q495

HIGH

GHSA-26wg-9xf2-q495 is a high-severity (CVSS 8.1) vulnerability in novu/api. A fix is available for novu/api — see the affected versions and patch details below.

Published

Apr 14, 2026

Updated

Apr 14, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Apr 14, 2026 · OSV.dev, FIRST.org (EPSS)

Real-World Exposure

1 pkg affected

📦novu/api

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects npm packages — download data is not available via public APIs for these ecosystems.

Description

Summary

XSS sanitization is incomplete, some attributes are missing such as oncontentvisibilityautostatechange=. This allows for the email preview to render HTML that executes arbitrary JavaScript,

Details

Sanitization is implemented here: https://github.com/novuhq/novu/blob/next/libs/application-generic/src/services/sanitize/sanitizer.service.ts

With allowedAttributes: false, all attributes are allowed through sanitize-html. Even dangerous ones like oncontentvisibilityautostatechange=. The DANGEROUS_ATTRIBUTES array tries to handle this by denying more attributes after the fact, but this list is incomplete. I copied all well-known payloads from: https://portswigger.net/web-security/cross-site-scripting/cheat-sheet And found that the oncontentvisibilityautostatechange= attribute isn't detected.

PS. there seems to also be another even more lax sanitizer here, but I wasn't able to figure out where it is used: https://github.com/novuhq/novu/blob/next/packages/framework/src/utils/sanitize.utils.ts

PoC

Create a new workflow and add an Email step
In the body, write the following HTML code:

<a oncontentvisibilityautostatechange="alert(window.origin)" style="display:block;content-visibility:auto">

Wait a second and notice the XSS popup showing the current origin:

https://dashboard.novu.co/env/dev_env_gVtdgDEhgf1CetwX/workflows/onboarding-demo-workflow_wf_gVtdh2uV0h7j3ffK/steps/email-step_st_gVtqdgIrOkYVvP9F/editor

Impact

This may look like a Self-XSS similar to https://github.com/novuhq/novu/security/advisories/GHSA-w8vm-jx29-52fr, but it can be more impactful. First of all, if multiple users can access this dashboard, the link above can directly bring the to the email step editor to trigger the XSS. An attacker can also use the Google/GitHub OAuth flows without completing the code callback step, and send that URL to the victim to intentionally log the vicitm into the attacker's account. If the attacker has prepared an XSS payload there, they will now be allowed to view it, so it triggers.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`novu/api`	all versions	3.15.0`npm install novu/api@3.15.0`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for novu/api, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update novu/api to 3.15.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-26wg-9xf2-q495 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

### Summary XSS sanitization is incomplete, some attributes are missing such as `oncontentvisibilityautostatechange=`. This allows for the email preview to render HTML that executes arbitrary JavaScript, ### Details Sanitization is implemented here: https://github.com/novuhq/novu/blob/next/libs/application-generic/src/services/sanitize/sanitizer.service.ts With `allowedAttributes: false`, all attributes are allowed through `sanitize-html`. Even dangerous ones like `oncontentvisibilityautostatechange=`. The `DANGEROUS_ATTRIBUTES` array tries to handle this by denying more attributes after t

O3 Security · Impact-Aware SCA

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