manage_proj_page.php in Mantis before 1.1.4 allows remote authenticated users to execute arbitrary code via a sort parameter containing PHP sequences, which are processed by create_function within the multi_sort function in core/utility_api.php.
The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.