WordPress Calendar 1.3.7 Cross Site Scripting

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Cross-Site Scripting in Calendar WordPress Plugin  
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Remco Vermeulen, July 2016  
  
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Abstract  
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A Cross-Site Scripting vulnerability was found in the Calendar 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-20160725-0008  
  
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Tested versions  
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This issue was successfully tested on Calendar WordPress Plugin version  
1.3.7.  
  
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Fix  
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This issue is resolved in Calendar version 1.3.8.  
  
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Details  
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https://sumofpwn.nl/advisory/2016/cross_site_scripting_in_calendar_wordpress_plugin.html  
  
For any page containing a calendar the GET request parameters are appended as hidden inputs when the calendar is configured to have a date switcher. The input isn't properly sanitised and allows an attacker to add attributes to the input, including events.  
  
In order to exploit this issue, the attacker has to lure/force a logged on WordPress Administrator into opening a malicious website. In addition, the calendar must configured to have a date switcher. By default this is disabled.  
Proof of concept  
  
Given the post hello-world, which has a calendar, visit the page with the following URL:  
  
http://<target>/2016/06/22/hello-world/?foo=whoeiii\%22%20accesskey=x%20onclick=alert(1);//  
  
The key combination CTRL + ALT + x triggers the onclick event.  
  
  
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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.  
  
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