Note Mark has Stored XSS via Unrestricted Asset Upload

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.7 · CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N

EPSS

• CVE-2026-40262: 0.31% estimated exploitation activity in the next 30 days; percentile 23.82 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary A stored same-origin XSS vulnerability allows any authenticated user to upload an HTML, SVG, or XHTML file as a note asset and have it executed in a victim’s browser under the application’s origin. Because the application serves these files inline without a safe content type and without nosniff, browsers can sniff and render active content, giving the attacker access to authenticated Note Mark API actions as the victim. Details This issue results from three compounding flaws in the asset handling and delivery path. 1. Asset delivery can be used as an attack vector The asset delivery route can be used to deliver attacker-controlled uploaded content directly to a victim by URL. Relevant route: - handlers/assets.go:40 This makes the uploaded asset reachable by direct navigation, which provides the delivery mechanism for the payload. 2. Text-based active content is served with an empty Content-Type The asset handler relies on h2non/filetype for content-type detection: -…

Published by the source

13 Apr 2026, 19:23 UTC

Last modified by the source

24 Apr 2026, 20:37 UTC

Source last checked

26 Oct 2026, 15:19 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-9pr4-rf97-79qh

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# Patch Next advisory brief: CVE-2026-40262

Advisory: Note Mark has Stored XSS via Unrestricted Asset Upload
IDs: CVE-2026-40262, GHSA-9pr4-rf97-79qh
Record: https://patchnext.com/advisories/cve-2026-40262 (revision 1, source checked 26 Oct 2026, 15:19 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/enchant97/note-mark/backend 0.0.0-20260411145018-6bb62842ccb9. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/enchant97/note-mark/backend: affected < 0.0.0-20260411145018-6bb62842ccb9; fixed in 0.0.0-20260411145018-6bb62842ccb9

## Suggested inspection (read-only)
- Go github.com/enchant97/note-mark/backend: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/enchant97/note-mark/backend.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-9pr4-rf97-79qh (GitHub-reviewed advisory GHSA-9pr4-rf97-79qh lists affected ranges: Go github.com/enchant97/note-mark/backend >=0 <0.0.0-20260411145018-6bb62842ccb9)

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