WordPress Add From Server 6.2 Cross Site Request Forgery

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Cross-Site Request Forgery vulnerability in Add From Server WordPress  
Plugin  
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Edwin Molenaar, July 2016  
  
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Abstract  
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It was discovered that Add From Server is vulnerabile to Cross-Site  
Request Forgery. It can be exploited by luring the target user into  
clicking a specially crafted link or visiting a malicious website (or  
advertisement). An attacker can use this issue to add illegal content to  
the victims server, or add very large files to the victim's server to  
exaust the amount of avalible disk space.  
  
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OVE ID  
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OVE-20160718-0004  
  
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Tested versions  
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These issues were successfully tested on Add From Server WordPress  
Plugin version 6.2.  
  
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Fix  
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This issue is resolved in Add From Server version 3.3.2.  
  
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Details  
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https://sumofpwn.nl/advisory/2016/cross_site_request_forgery_vulnerability_in_add_from_server_wordpress_plugin.html  
  
When a (media) file is added from the server, the source is not validated. This means that not only files from the localhost can be added, but also from other sources. The affected code is not protected with an anti-Cross-Site Request Forgery token.  
  
The function handle_imports() only removes slashes. The vulnerability exists in the file add-from-server/class.add-from-server.php (line 213). Because slashes are removed, the file that will be uploaded must exist in the server root. For example: www.example.com/largefile.txt  
  
The host and filename will be set in a separate parameter, so no slashes are needed.  
  
  
Proof of concept  
  
POST /wp-admin/upload.php?page=add-from-server HTTP/1.1  
Host: <target>  
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8  
Connection: close  
Content-Type: application/x-www-form-urlencoded  
  
files%5B%5D=largefile.txt&import-date=current&cwd=www.example.com&import=Import  
  
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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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