Convert Plus WordPress plugin flaw allows hackers to create Admin accounts

The WordPress plugin Convert Plus is affected by a critical flaw that could be exploited by an unauthenticated attacker to create accounts with administrator privileges.

The WordPress plugin Convert Plus is affected by a critical vulnerability that could be exploited by an unauthenticated attacker to create accounts with administrator privileges.

A vulnerability ties with the lack of filtering when processing a new user subscription via a form implemented by the Convert Plus plugin that already has more than 100,000 active installations,

Convert Plus aims at generating more subscribers and sales conversions using popups, header & footer bars, slide-in forms, sidebar widgets, in-line forms, and social buttons.

New subscribers can use a specific form that allows them to define the role they want, of course, administrator accounts are not in the list of possible options og a drop-down menu.

Experts at Defiant discovered that Convert Plus plugin includes an administrator role in a hidden field called “cp_set_user.” Experts pointed out that the value for this field could be supplied by the same HTTP request as the rest of the subscription entry, and users can modify it.

“However, in vulnerable versions of the plugin, this intended user role wasn’t fetched from the database on submission. Instead, this setting was reflected in a hidden field on the plugin’s forms called cp_set_user.” reads the analysis by the experts. “Because this value is supplied by the same HTTP request as the rest of the subscription entry, it can be modified by the user.”

It could very easy for an attacker to submit a subscription form and modify the value of the “cp_set_user” by setting the “administrator” value to create a new admin user.

“This code calls the plugin’s function cp_add_new_user_role with the role provided in the AJAX request, which then handles the process of creating the user as directed.” continues the analysis.

“Since no filtering is applied when this new subscription is processed, if an attacker submits a subscription form and changes the value of cp_set_user to “administrator”, the plugin will create an administrator user associated with the given email address.”

The hack allows to create a new admin account with a randomized password, but it is not a problem because the attacker can use a classic password reset procedure to change the password too.

The vulnerability affects all versions of the Convert Plus plugin up to 3.4.2., it is essential for administrators to update their install to the version 3.4.3.

Defiant experts also published a video PoC for the exploitation of the issue.

Below the disclosure timeline of the vulnerability:

• May 24 – Vulnerability discovered. Notified developers privately.
• May 28 – Patch released by developers. Firewall rule released for Premium users.
• June 27 – Planned date for firewall rule’s release to Free users.

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Pierluigi Paganini

(SecurityAffairs – Convert Plus plugin, hacking)

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