MODX Revolution version <=2.6.4 contains a Incorrect Access Control vulnerability in Filtering user parameters before passing them into phpthumb class that can result in Creating file with custom a filename and content. This attack appear to be exploitable via Web request. This vulnerability appears to have been fixed in commit 06bc94257408f6a575de20ddb955aca505ef6e68.
https://rudnkh.me/posts/critical-vulnerability-in-modx-revolution-2-6-4
https://github.com/modxcms/revolution/pull/13979
https://github.com/modxcms/revolution/commit/06bc94257408f6a575de20ddb955aca505ef6e68