GHSA-26wg-9xf2-q495
HIGHNovu has a XSS sanitization bypass
Blast Radius
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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:
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
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | novu/api | all versions | 3.15.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for novu/api. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
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
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether GHSA-26wg-9xf2-q495 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to GHSA-26wg-9xf2-q495. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-26wg-9xf2-q495 in your dependencies?
O3 detects GHSA-26wg-9xf2-q495 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.