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.
A security feature bypass exists in Azure SSH Keypairs, due to a change in the provisioning logic for some Linux images that use cloud-init, aka 'Azure SSH Keypairs Security Feature Bypass Vulnerability'.