CVE-2020-15187: plugin.yaml file allows for duplicate entries in helm

During a security audit of Helm’s code base, Helm maintainers identified a bug in which a Helm plugin can contain duplicates of the same entry, with the last one always used. If a plugin is compromised, this lowers the level of access that an attacker needs to modify a plugin’s install hooks, causing a local execution attack.

To perform this attack, an attacker must have write access to the git repository or plugin archive (.tgz) while being downloaded (which can occur during a MITM attack on a non-SSL connection).