HomeBox is a home inventory and organization system. Prior to 0.27.0, the maybeUrl() utility accepts markdown-style links in entity custom-field values without restricting the URL scheme, so an authenticated user can store a javascript: URI that is rendered as a clickable anchor on an item page. When another authenticated user clicks the link, attacker-controlled JavaScript executes in the victim's HomeBox origin, enabling session theft, account takeover, or data exfiltration. This issue is fixed in version 0.27.0.