There is 1 open security issue in buster.
1 issue left for the package maintainer to handle:
PuTTY 0.68 through 0.73 has an Observable Discrepancy leading to an information leak in the algorithm negotiation. This allows man-in-the-middle attackers to target initial connection attempts (where no host key for the server has been cached by the client).
You can find information about how to handle this issue in the security team's documentation.