New Joomla Exploit CVE-2015-8562 - NGINX

There is a new zero day exploit in Joomla. Details are described in CVE-2015-8562.

We recommend that you update Joomla immediately, but if you cannot do that or cannot change the files on your backend servers, you can apply a fix in NGINX or NGINX Plus on the frontend.

Note: We strongly advise to update your Joomla installations as soon as possible, even if you patch your site today with this NGINX configuration.

You can read about the exploit and the patch at the Sucuri blog or Ars Technica, among others.

Identifying the Attack

The original attacks came from these IP addresses:

• On 12 December 2015 – 74.3.170.33
• On 13 December 2015 – 146.0.72.83 and 194.28.174.106

The attack is usually performed by modifying the User-Agent header and can be identified by these values inside the header: JDatabaseDriverMysqli and O: (capital letter O followed by the colon).

Joomla provides the following sample log entry from an attack.

2015 Dec 12 16:49:07 clienyhidden.access.log
Src IP: 74.3.XX.XX / CAN / Alberta
74.3.XX.XX [12/Dec/2015:16:49:40 -0500] GET /contact/ HTTP/1.1 403 5322 http://google.com/ }__test|O:21:x22JDatabaseDriverMysqlix22:3:..{s:2:x22fcx22;O:17:x22JSimplepieFactoryx22:0:..{}s:21:x22x5C0x5C0x5C0disconnectHandlersx22;a:1:{i:0;a:2:{i:0;O:9:x22SimplePiex22:5:..{s:8:x22sanitizex22;O:20:x22JDatabaseDriverMysqlx22:0:{}s:8:x22feed_urlx22;s:60:..

Applying a Fix in NGINX or NGINX Plus

Use this snippet of NGINX configuration to block the original IP addresses and any request where the User-Agent header contains O: or JDatabaseDriverMysqli. To block additional IP addresses, add them to the list in the second map block.

http {
    map $http_user_agent $blocked_ua {
        ~(?i)O: 1;
        ~(?i)JDatabaseDriverMysql 1;
        default 0;
    }

    map $remote_addr $blocked_ip {
        74.3.170.33 1;
        146.0.72.83 1;
        194.28.174.106 1;
        default 0;
    }
    
    server {
        listen 80;
        if ($blocked_ua) { return 403; }
        if ($blocked_ip) { return 403; }
        # ...
    }
}

For further information, see this article on how to restrict access to your site.

Post your experience in the Comments below.