There is 1 open security issue in buster.
1 issue left for the package maintainer to handle:
An issue was discovered in KDE KMail before 19.12.3. By using the proprietary (non-RFC6068) "mailto?attach=..." parameter, a website (or other source of mailto links) can make KMail attach local files to a composed email message without showing a warning to the user, as demonstrated by an attach=.bash_history value.
You can find information about how to handle this issue in the security team's documentation.