Yesterday we disclosed a large malware campaign targeting and compromising over 100,000 WordPress sites, and growing by the hour. It was named SoakSoak due to the first domain used in the malware redirection path (soaksoak.ru).

After a bit more time investigating this issue, we were able to confirm that the attack vector is the RevSlider plugin. We disclosed a serious vulnerability with this plugin a few months ago, it seems that many webmasters have either not heard of or did not take seriously the vulnerability.

The biggest issue is that the RevSlider plugin is a premium plugin, it’s not something everyone can easily upgrade and that in itself becomes a disaster for website owner. Some website owners don’t even know they have it as it’s been packaged and bundled into their themes. We’re currently remediating thousands of sites and when engaging with our clients many had no idea the plugin was even within their environment.

The Attack Sequence

We have investigated thousands of compromised sites with this injection and based on the logs, we are able to confirm the exact attack vector being targeted.

1. Discovery: There appears to be an initial reconnaissance scan occurring where the attacker[s] are looking to see if the file exists. Snippet of the code

94.153.8.126 – – [14/Dec/2014:09:59:35 -0500] “GET /wp-content/plugins/revslider/rs-plugin/font/revicons.eot HTTP/1.1″ 200

94.190.20.83 – – [14/Dec/2014:00:12:07 -0500] “GET /wp-admin/admin-ajax.php?action=revslider_show_image&img=../wp-config.php HTTP/1.0″ 202

The first entry looks for the revicons.eot files and the second one attempts to use one of the Revslider vulnerabilities to download the wp-config.php file.

2. Exploit:If the discovery phase is successful and they find a site using Revslider, they use a second vulnerability in Revslider and attempt to upload a malicious theme to the site:
   

   94.153.8.126 – – [14/Dec/2014:04:31:28 -0500] “POST /wp-admin/admin-ajax.php HTTP/1.1″ 200 4183 “-”
   Content-Disposition: form-data; revslider_ajax_action
   update_plugin; name=”update_file”;…

3. Take over: If the exploit is successful, they inject the popular Filesman backdoor into the website, which they access directly at /wp-content/plugins/revslider/temp/update_extract/revslider/update.php this provides full access by circumventing existing access controls:
   

   94.153.8.126 – – [14/Dec/2014:04:31:28 -0500] “GET /wp-content/plugins/revslider/temp/update_extract/revslider/update.php HTTP/1.1″ 200 5287
   “-” “Mozilla/5.0 (Windows NT 5.1; rv:33.0) Gecko/20100101 Firefox/33.0″

From there, they inject a secondary backdoor that modifies the swfobject.js file and injects the malware redirecting site visitors to soaksoak.ru.

This campaign is also making use of a number of new backdoor payloads, some are being injected into images to further assist evasion and others are being used to inject new administrator users into the WordPress installs, giving them even more control long term. Some users are clearing infections and getting reinfected within minutes and the reason is because of the complex nature of the payloads and improper cleaning efforts.

Do not just clean these 2 files!

We are hearing a lot of recommendations online to just replace the swfobject.js and template-loader.php files to remove the infection.

It does removes the infection, but does not address the left over backdoors and initial entry points. The website will be reinfected quickly. If you are affected by this, expect to find yourself riddled with backdoors and infections, you have to not only clean, but also stop all malicious attacks. You can stop malicious attacks through the use of a Website Firewall, ours or someone else, just use a Firewall, a real one preferably.

Via Sucuri.net