SeriousSAM vulnerability, tracked as CVE-2021-36934, exists in the default configuration of Windows 10 and Windows 11, specifically due to a setting that allows 'read' permissions to the built-in user's group that contains all local users.
As a result, built-in local users have access to read the SAM files and the Registry, where they can also view the hashes. Once the attacker has 'User' access, they can use a tool such as Mimikatz to gain access to the Registry or SAM, steal the hashes and convert them to passwords. Invading Domain users that way will give attackers elevated privileges on the network.
Because there is no official patch available yet from Microsoft, the best way to protect your environment from SeriousSAM vulnerability is to implement hardening measures.