Joplin: Stored XSS via inline-served note attachment on published shares

Joplin is an open source note-taking and to-do application that organises notes and lists into notebooks. Prior to 3.7.7, Joplin Server's GET /shares/:id?resource_id= route serves a resource with the attacker-controlled mime value and omits Content-Disposition when the resource title is empty. A low-privileged user can publish an empty-title image/svg+xml attachment whose script executes when a victim opens the public share. By default, user content shares the Joplin Server application origin, allowing the script to access same-origin data and, when the victim is authenticated, perform actions with the victim's session, including reading administrative data and anti-CSRF tokens. Installations that configure USER_CONTENT_BASE_URL to a separate origin still execute the script, but on that separate user-content origin rather than the application origin. This issue is fixed in version 3.7.7.