Marc-Alexandre Montpas, from our research team, found a serious security vulnerability in the MailPoet WordPress plugin. This bug allows an attacker to upload any file remotely to the vulnerable website (i.e., no authentication is required).

This is a serious vulnerability, The MailPoet plugin (wysija-newsletters) is a very popular WordPress plugin (over 1,700,000 downloads). This vulnerability has been patched, if you run the WordPress MailPoet plugin please upgrade ASAP!

Are you affected?

If you have this plugin activated on your website, the odds are not in your favor. An attacker can exploit this vulnerability without having any privileges/accounts on the target site. This is a major threat, it means every single website using it is vulnerable.

The only safe version is the 2.6.7, this was just released a few hours ago (2014-Jul-01).

Why is it so dangerous?

This bug should be taken seriously, it gives a potential intruder the power to do anything he wants on his victim’s website. It allows for any PHP file to be uploaded. This can allow an attacker to use your website for phishing lures, sending SPAM, host malware, infect other customers (on a shared server), and so on!!

Technical Details

Our research team discovered this flaw a few weeks ago and immediately disclosed it to the MailPoet team. They responded very well and released a patch as quickly as possible.

Because of the nature of the vulnerability, specifically it’s severity, we will not be disclosing additional technical details. The basics of the vulnerability however is something all plugin developers should be mindful of: the vulnerability resides in the fact that the developers assumed that WordPress’s “admin_init” hooks were only called when an administrator user visited a page inside /wp-admin/.

It is a easy mistake to make and they used that hook (admin_init) to verify if a specific user was allowed to upload files.

However, any call to /wp-admin/admin-post.php also executes this hook without requiring the user to be authenticated. Thus making their theme upload functionality available to everybody.

Pro-tip: If you are a developer, never use admin_init() (or is_admin()) as an authentication method.

How should you protect yourself?

Again, Update the plugin as soon as possible. Keeping WordPress and all plugins updated is the first step to keep your sites secured.

For our customers: The good news is that any website behind our Website Firewall – CloudProxy has been protected against this vulnerability since we found it.

Via Sucuri.net