Versions of MCollective prior to 2.10.4 deserialized YAML from agents without calling safe_load, allowing the potential for arbitrary code execution on the server. The fix for this is to call YAML.safe_load on input. This has been tested in all Puppet-supplied MCollective plugins, but there is a chance that third-party plugins could rely on this insecure behavior.
Gentoo Linux Security Advisory 201709-1 - A vulnerability in MCollective might allow remote attackers to execute arbitrary code. Versions less than 2.11.0 are affected.