A user able to create Policy Sets can run arbitrary code by sending malicious Groovy scripts which will escape the configured Groovy sandbox.
Eclipse Keti is a service that was designed to protect RESTfuls API using Attribute Based Access Control (ABAC). In Keti a sandbox escape vulnerability may lead to post-authentication Remote Code execution. This vulnerability is known to exist in the latest commit at the time of writing this CVE (commit a1c8dbe). For more details see the referenced GHSL-2021-063.