FCKEditor Core ASP 2.6.8 - Arbitrary File Upload Protection Bypass

- Title: FCKEditor 2.6.8 ASP Version File Upload Protection bypass
- Credit goes to: Mostafa Azizi, Soroush Dalili
- Link: http://sourceforge.net/projects/fckeditor/files/FCKeditor/
- Description:
There is no validation on the extensions when FCKEditor 2.6.8 ASP version is 
dealing with the duplicate files. As a result, it is possible to bypass 
the protection and upload a file with any extension.

- Reference: http://soroush.secproject.com/blog/2012/11/file-in-the-hole/
- Solution: Please check the provided reference or the vendor website.
- PoC: http://www.youtube.com/v/1VpxlJ5jLO8?version=3&hl=en_US&rel=0&vq=hd720

Duplicate files do not have proper validation on their extensions.

As a result, it is possible to upload any file with any extension on the server by using Null Character.

Applications on IIS6 can also use "file.asp;gif" pattern.
- Solution: In "config.asp", wherever you have: ConfigAllowedExtensions.Add "File","EXTENSION HERE" Change it to: ConfigAllowedExtensions.Add "File","^(Extensions HERE)$"
- Vulnerability: Vulnerable File: commands.asp Function: FileUpload() Vulnerable Code: sFileName = RemoveExtension( sOriginalFileName ) & "(" & iCounter & ")." & sExtension




Note: Quick patch for FCKEditor 2.6.8 File Upload Bypass:

In “config.asp”, wherever you have:

      ConfigAllowedExtensions.Add    “File”,”Extensions Here”

Change it to:

      ConfigAllowedExtensions.Add    “File”,”^(Extensions Here)$”