Home Assistant before 2021.1.3 does not have a protection layer that can help to prevent directory-traversal attacks against custom integrations. NOTE: the vendor's perspective is that the vulnerability itself is in custom integrations written by third parties, not in Home Assistant; however, Home Assistant does have a security update that is worthwhile in addressing this situation
https://www.home-assistant.io/blog/2021/01/22/security-disclosure/
https://www.home-assistant.io/blog/2021/01/14/security-bulletin/