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Stored Cross-Site Scripting in WP Canvas - Shortcodes WordPress Plugin
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Yorick Koster, July 2016

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Abstract
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A Cross-Site Scripting vulnerability was found in the WP Canvas -
Shortcodes WordPress Plugin. This issue allows an attacker to perform a
wide variety of actions, such as stealing Administrators' session
tokens, or performing arbitrary actions on their behalf. This issue can
be exploited by authenticated users with the Contributor or higher role.

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OVE ID
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OVE-20160724-0031

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Tested versions
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This issue was successfully tested on WP Canvas - Shortcodes WordPress
Plugin version 1.92.

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Fix
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This issue has been addressed in WP Canvas - Shortcodes WordPress Plugin
version 2.07.

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Details
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https://sumofpwn.nl/advisory/2016/stored_cross_site_scripting_in_wp_canvas___shortcodes_wordpress_plugin.html

This issue exists due to the lack of validation on the url attributed of the wc_button shortcode. A Contributor or higher can create a button with a specially crafted Javascript payload. When a (logged) on user clicks on this button, the payload will be executed. This bypasses the unfiltered_html privilege of WordPress, which is normally only assigned to Editors & Administrators.

Proof of concept

[wc_button type="primary" url="javascript:alert(1)" title="Visit Site" target="self" position="float"]Sample Content[/wc_button]


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Summer of Pwnage (https://sumofpwn.nl) is a Dutch community project. Its
goal is to contribute to the security of popular, widely used OSS
projects in a fun and educational way.