WordPress Plugin Nelio AB Testing Server-Side Request Forgery (SSRF)

## Case Study: SSRF in Nelio AB Testing WordPress Plugin ## Nelio AB Testing is a WordPress plugin used for A/B Testing in WordPress pages. We can download the source-code of the Plugin from plugins.svn.wordpress.org/nelio-ab-testing/tags/4.5.8/. Server-side Request Forgery (SSRF) is a vulnerability where requests can be made from the vulnerable server to the intra/internet. Though it does not seem to have serious impact, using a protocol supported by certain URI schemes, an attacker could collect various information about the server or even achieve remote code execution (RCE). There is a very comprehensive cheat-sheet for SSRF available here. Zooming in to the vulnerable PHP script at .`/ajax/iesupport.php`. It is obvious from manual analysis that we are able to control the URL that would eventually be cURL’ed by the server. <?php ** Truncated ** $url = false; $data = false; if ( isset( $_POST['originalRequestUrl'] ) ) { $url = $_POST['originalRequestUrl']; $url = preg_replace( '/^\/\//', '', $url ); } else { // Silence is gold return; } if ( isset( $_POST['data'] ) ) { $data = $_POST['data']; } else { // Silence is gold return; } $was_data_sent = false; if ( !$was_data_sent && function_exists( 'curl_version' ) ) { //open connection $ch = curl_init(); if ( $ch ) { //set the url, number of POST vars, POST data curl_setopt( $ch, CURLOPT_URL, $url ); curl_setopt( $ch, CURLOPT_POST, substr_count( $data, '=' ) ); curl_setopt( $ch, CURLOPT_POSTFIELDS, $data ); if ( isset( $_SERVER['HTTP_REFERER'] ) ) curl_setopt( $ch, CURLOPT_REFERER, $_SERVER['HTTP_REFERER'] ); if ( isset( $_SERVER['HTTP_USER_AGENT'] ) ) curl_setopt( $ch, CURLOPT_USERAGENT, $_SERVER['HTTP_USER_AGENT'] ); //execute post $result = curl_exec( $ch ); //close connection curl_close( $ch ); $was_data_sent = true; } } ** Truncated ** ?> In fact, the vulnerabilty was found by the tool automatically. We can see an intuitive result from testing the vulnerable script on http://taint.spro.ink. We see that the tool is able to detect the tainted user-input being used in the `curl_setopt` function.  From https://pluginu.com/nelio-ab-testing/, we can easily see that there are at least 173 websites using this plugin currently! Being lucky, I was able to find a bug bounty program that has a WordPress site using this particular plugin and was able to obtain a bounty with this finding. :)  ## Conclusion ## What this experiment proved was that it was highly possible for a development cycle/process where applications are continuously tested for vulnerability. However, more work needs to be done to ensure true positives in result and/or to even automatically patch simple vulnerabilities! This is the first part of many and in the subsequent parts I will write more about the tool in detail! Thanks for reading!