CVE-2026-40262 Note Mark has Stored XSS via Unrestricted Asset Upload
An attacker can upload malicious HTML or SVG files that execute JavaScript in victims' browsers, potentially stealing sessions or performing actions.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-40262?
CVE-2026-40262 is a high-severity cross-site scripting vulnerability in enchant97 note-mark, published on 16 Apr 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.
Official description
Note Mark is an open-source note-taking application. In versions 0.19.1 and prior, the asset delivery handler serves uploaded files inline and relies on magic-byte detection for content type, which does not identify text-based formats such as HTML, SVG, or XHTML. These files are served with an empty Content-Type, no X-Content-Type-Options: nosniff header, and inline disposition, allowing browsers to sniff and render active content. An authenticated user can upload an HTML or SVG file containing JavaScript as a note asset, and when a victim navigates to the asset URL, the script executes under the application's origin with access to the victim's authenticated session and API actions. This issue has been fixed in version 0.19.2.
Which versions are affected by CVE-2026-40262?
3 open source packages ship an affected version, including github.com/enchant97/note-mark/backend.
| Package | Affected | Fixed in |
|---|---|---|
github.com/enchant97/note-mark/backend Go | All versions | 0.0.0-20260411145018-6bb62842ccb9 |
github.com/enchant97/note-mark/backend Go | All versions | 0.0.0-20260411145018-6bb62842ccb9 |
github.com/enchant97/note-mark/backend Go | All versions | 0.0.0-20260411145018-6bb62842ccb9 |
How do I fix CVE-2026-40262?
Upgrade github.com/enchant97/note-mark/backend to 0.0.0-20260411145018-6bb62842ccb9 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-40262 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40262 exists.
Sources
Also known as GHSA-9pr4-rf97-79qh, GO-2026-5295.