CVE-2020-25717

A flaw was found in the way Samba maps domain users to local users. An authenticated attacker could use this flaw to cause possible privilege escalation.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Setting "gensec:require_pac=true" in the smb.conf makes, due to a cache prime in winbind, the DOMAIN\user lookup succeed, provided nss_winbind is in use, 'winbind use default domain = no' (the default) and no error paths are hit.

It would be prudent to pre-create disabled users in Active Directory matching on all privileged names not held in Active Directory, eg

 samba-tool user add root -H ldap://$SERVER -U$USERNAME%$PASSWORD --random-password
 samba-tool user add ubuntu -H ldap://$SERVER -U$USERNAME%$PASSWORD --random-password

(repeat for eg all system users under 1000 in /etc/passwd or special to any other AD-connected services, eg perhaps "admin" for a web-app)