document-merge-service vulnerable to Remote Code Execution via Server-Side Template Injection

Document Merge Service is a document template merge service providing an API to manage templates and merge them with given data. Versions 6.5.1 and prior are vulnerable to remote code execution via server-side template injection which, when executed as root, can result in full takeover of the affected system. As of time of publication, no patched version exists, nor have any known workarounds been disclosed.