Note Mark is an open-source note-taking application. From 0.13.0 to before 0.19.4, the Note Mark application allows authenticated users to upload assets to notes via POST /api/notes/{noteID}/assets, where the asset filename is provided through the X-Name HTTP request header. This value is stored directly in the database without any sanitization or validation - no path separator filtering, no directory traversal sequence rejection, and no use of filepath.Base() to strip directory components. The unsanitized name is persisted as-is in the note_assets table (Name column, varchar(80)). When an administrator subsequently runs the data export CLI commands (note-mark migrate export-v1 or note-mark migrate export), the stored asset name is passed directly into filepath.Join() and path.Join() calls as part of the output file path argument to os.Create(). Since Go's filepath.Join() resolves ../ sequences during path normalization, an attacker-controlled asset name containing directory traversal sequences causes the export process to write files to arbitrary locations on the filesystem, completely outside the intended export directory. This vulnerability is fixed in 0.19.4.

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

### Description

The Note Mark application allows authenticated users to upload assets to notes via `POST /api/notes/{noteID}/assets`, where the asset filename is provided through the `X-Name` HTTP request header. This value is stored directly in the database without any sanitization or validation - no path separator filtering, no directory traversal sequence rejection, and no use of `filepath.Base()` to strip directory components. The unsanitized name is persisted as-is in the `note_assets` table (`Name` column, `varchar(80)`).

When an administrator subsequently runs the data export CLI commands (`note-mark migrate export-v1` or `note-mark migrate export`), the stored asset name is passed directly into `filepath.Join()` and `path.Join()` calls as part of the output file path argument to `os.Create()`. Since Go's `filepath.Join()` resolves `../` sequences during path normalization, an attacker-controlled asset name containing directory traversal sequences causes the export process to write files to arbitrary locations on the filesystem, completely outside the intended export directory.

The export process typically runs as root (the default in Docker deployments and common in bare-metal setups). This means the arbitrary file write operates with root privileges, allowing an attacker to write to any writable location on the filesystem. This can be escalated to Remote Code Execution by overwriting system binaries such as `/bin/bash` with a malicious payload. Since the Go binar…