An issue was discovered in HestiaCP before v1.3.5. Attackers are able to arbitrarily install packages due to values taken from the pgk [] parameter in the update request being transmitted to the operating system's package manager.
https://github.com/hestiacp/hestiacp/commit/9a1fccd37f2842fdf96ffb48895c4bfa9788c469
https://github.com/hestiacp/hestiacp/commit/27556a9a43aeaf308b33be224c2e70f2011574e6