Language: PHP
Label: vulnerable
CWE: CWE-77 \u2014 Improper Neutralization of Special Elements used in a Command ('Command Injection')
The product constructs all or part of a command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended command when it is sent to a downstream component.

Code:
function get_path_ext($path){
	$name = get_path_this($path);
	$ext = '';
	if(strstr($name,'.')){
		$ext = substr($name,strrpos($name,'.')+1);
		$ext = strtolower($ext);
	}
	if (strlen($ext)>3 && preg_match("/([\x81-\xfe][\x40-\xfe])/", $ext, $match)) {
		$ext = '';
	}
	return htmlspecialchars($ext);
}