WordPress File Delete to Code Execution Vulnerability

WordPress is the most popular CMS on the web. According to w3tech, it is used by approximately 30% of all websites¹. This wide adoption makes it an interesting target for cyber criminals. In this blog post we are going to introduce an authenticated arbitrary file deletion vulnerability in the WordPress core that can lead to attackers executing arbitrary code. The vulnerability was reported 7 months ago to the WordPress security team but still remains unpatched. The long time elapsed since the initial reporting without any patch or concrete plans has led us to the decision to make it public.

Affected WordPress Versions

Any WordPress version, including the current 4.9.6 version, is susceptible to the vulnerability described in this blogpost.

Exploiting this Vulnerability

For exploiting the vulnerability discussed in the following an attacker would need to gain the privileges to edit and delete media files beforehand. Thus, the vulnerability can be used to escalate privileges attained through the takeover of an account with a role as low as Author, or through the exploitation of another vulnerability/misconfiguration.

What can an attacker do

Exploiting the vulnerability grants an attacker the capability to delete any file of the WordPress installation (+ any other file on the server on which the PHP process user has the proper permissions to delete). Besides the possibility of erasing the whole WordPress installation, which can have desastrous consequences if no current backup is available, an attacker can make use of the capability of arbitrary file deletion to circumvent some security measures and to execute arbitrary code on the webserver. More precisely, the following files can be deleted:

• .htaccess: In general, deleting this file does not have any security consequences. However, in some occasions, the .htaccess file contains security related constraints (e.g., access constraints to some folders). Deleting this file would deactivate those security constraints.
• index.php files: Oftentimes empty index.php files are placed into directories to prevent directory listing for the case the webserver fails to do so. Deleting those files would grant an attacker a listing of all files in directories protected by this measure.
• wp-config.php: Deleting this file of a WordPress installation would trigger the WordPress installation process on the next visit to the website. This is due to the fact that wp-config.php contains the database credentials, and without its presence, WordPress acts as if it hasn’t been installed yet. An attacker could delete this file, undergo the installation process with credentials of his choice for the administrator account and, finally, execute arbitrary code on the server.

Patch and Fix this Error

The WordPress team published an update in their security and maintenance release 4.9.7 that fixes the vulnerability described in this blog post and a related one discovered later by Wordfence.

Full information about this Vulnerability including technical details can be found here at The RipsTech Blog