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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 WordPress
Plugin version 1.8.9.3.

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Fix
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This issue is resolved in commit d39a18b.
https://github.com/strangerstudios/paid-memberships-pro/commit/d39a18b3e9fd373665a23e5e79e8caff77a3e7f4

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

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

More info on XSS

"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.

Proof of concept

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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