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Cross-Site Scripting vulnerability in Paid Memberships Pro WordPress
Plugin
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Burak Kelebek, July 2016

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Abstract
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A Cross-Site Scripting vulnerability was found in the Paid Memberships
Pro 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. In order to exploit this
issue, the attacker has to lure/force a logged on WordPress
Administrator into opening a malicious website.

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OVE ID
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OVE-20160714-0015

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Tested versions
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This issue was successfully tested on Paid Memberships Pro [2] WordPress
Plugin version 1.8.9.3.

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Fix
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This issue is resolved in commit d39a18b [3].

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Introduction
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Details
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Cross-Site Scripting (XSS) attacks are a type of injection, in which
malicious scripts are injected into otherwise benign and trusted web
sites. XSS attacks occur when an attacker uses a web application to send
malicious code, generally in the form of a browser side script, to a
different end user. Flaws that allow these attacks to succeed are quite
widespread and occur anywhere a web application uses input from a user
within the output it generates without validating or encoding it.
Reflected XSS occurs when user input is immediately returned by a web
application in an error message, search result, or any other response
that includes some or all of the input provided by the user as part of
the request

"plugin_status" field does not validate <script> tags and does not
perform output encoding.

paid-memberships-pro/adminpages/addons.php
72: echo echo
admin_url("admin.php?page=pmpro-addons&force-check=1&plugin_status=" .
$status); 
33: $status = $_REQUEST['plugin_status']; 

An attacker needs to lure a logged-in admin to follow the link in the
proof of concept below. 

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Proof of concept
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http://<targetsite>/wp-admin/admin.php?page=pmpro-addons&plugin_status=foofoo%5C%22%3E%3Cscript%3Ealert%281%29%3C%2Fscript%3E%3Ca
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References
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[1]
https://sumofpwn.nl/advisory/2016/cross_site_scripting_vulnerability_in_paid_memberships_pro_wordpress_plugin.html
[2] https://wordpress.org/plugins/paid-memberships-pro/
[3]
https://github.com/strangerstudios/paid-memberships-pro/commit/d39a18b3e9fd373665a23e5e79e8caff77a3e7f4