Flask-AppBuilder is an application development framework built on top of Flask. Versions prior to 4.6.2 would allow for a malicious unauthenticated actor to perform an open redirect by manipulating the Host header in HTTP requests. Flask-AppBuilder 4.6.2 introduced the "FAB_SAFE_REDIRECT_HOSTS" configuration variable, which allows administrators to explicitly define which domains are considered safe for redirection. As a workaround, use a reverse proxy to enforce trusted host headers.