Carbon is an international PHP extension for DateTime. Application passing unsanitized user input to Carbon::setLocale are at risk of arbitrary file include, if the application allows users to upload files with .php extension in an folder that allows include or require to read it, then they are at risk of arbitrary code ran on their servers. This vulnerability is fixed in 3.8.4 and 2.72.6.
The PHP application receives input from an upstream component, but it does not restrict or incorrectly restricts the input before its usage in "require," "include," or similar functions.