GXCMS V1.5 has a file upload vulnerability in the background. The vulnerability is the template management page. You can edit any template content and then rename to PHP suffix file, after calling PHP file can control the server.
https://github.com/breezety/gxcms15/issues/1
https://github.com/ZackSecurity/VulnerReport/blob/cve/gxcms/1.md