When instructing cloud-init to set a random password for a new user account, versions before 21.2 would write that password to the world-readable log file /var/log/cloud-init-output.log. This could allow a local user to log in as another user.
Exploitability
AV:LAC:LPR:LUI:NScope
S:UImpact
C:HI:NA:N5.5/CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:NInformation Disclosure