EUVD-2026-291883

fkie_cve-2026-40262

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.

GHSA-9pr4-rf97-79qh — Note Mark has Stored XSS via Unrestricted Asset Upload

Affected: Go: github.com/enchant97/note-mark/backend

### 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`

```go huma.Get(api, "/api/notes/{noteID}/assets/{assetID}", h.GetNoteAssetContentByID) ```

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:

- `handlers/assets.go:147`

```go kind, _ := filetype.Match(buf) if kind != filetype.Unknown { contentType = kind.MIME.Value } ```

The detection library uses magic-byte matching and does not identify text-based formats such as HTML, SVG, JavaScript, XML, or XHTML. For those files, `filetype.Match` returns `Unknown`, leaving `Content-Type` unset or empty.

As a result, uploaded act…

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EUVD-2026-291883

fkie_cve-2026-40262

GHSA-9pr4-rf97-79qh — Note Mark has Stored XSS via Unrestricted Asset Upload