Configure the Default Policies of iptables to DROP Properly

Generally, iptables policies can be configured in allowlist or blocklist mode. You are advised to configure iptables policies in allowlist mode. Connections that do not comply with the rules in the allowlist are prohibited. Therefore, you can configure the DROP or REJECT policy for the INPUT,...

vino-preferences does not warn about UPnP especially with no password and no confirmation.

Vino, possibly before 3.2, does not properly document that it opens ports in UPnP routers when the "Configure network to automatically accept connections" setting is enabled, which might make it easier for remote attackers to perform further attacks...