There is 1 open security issue in buster.
1 issue left for the package maintainer to handle:
The Debian courier-authlib package before 0.71.1-2 for Courier Authentication Library creates a /run/courier/authdaemon directory with weak permissions, allowing an attacker to read user information. This may include a cleartext password in some configurations. In general, it includes the user's existence, uid and gids, home and/or Maildir directory, quota, and some type of password information (such as a hash).
You can find information about how to handle this issue in the security team's documentation.