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Mail Drives Security Considerations



Mail Drives Security Considerations
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Author: Attila Gerendi (Darkz)
Date: November 03, 2006 


 There are more "mail drive" solutions available like "GMail Drive", "GSpace", 
"Gmail FS", etc.. These systems are built to store ordinary files in email 
accounts (usually gmail because it's free 2Gb++ space). 

 In some of these solutions the files and folders usually are stored as 
attachments in a special email. The file system does not have FAT (File 
Allocation Table) and the informations regarding the name and path of the 
files/folders are stored in the email SUBJECT field. Additionally there is no 
mechanism to filter these emails.
 
 So the problem is the remote attacker can shout blindly emails which describe 
a file or folder in this file systems and manipulate or inject files into that 
file system. This may be used for a new spam type or to inject 
undesirable/malicious files into someone's file collection. At the first sight 
this can not be worse then plain email spamming, however because this concept 
is extending the email use if no sanitation will be included then it will 
extend the spam use as well, some malicious people will find out new malicious 
solutions for particular or generic situations.

A few examples are described below, other may exist.

1. viksoe's GMail Drive shell extension
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        - file injection. You can inject files into the "GMail Drive file 
system" by sending email with Subject: "GMAILFS: /new_filename.txt [13;a;1]" 
and "new_filename.txt" as attachment. However if the sender is not "self" then 
the filename will be displayed with red color. The sender email address can be 
spoofed.
        
        - folder creation. You can create new folder by sending email with 
Subject: "GMAILFS: /new_folder/. [14;a;1]"
        
        - rewrite file contains. You can overwrite file displayed content 
sending email with Subject: "GMAILFS: /existing_path/existing_filename.txt 
[13;a;1]" and "filename.txt" as attachment. However if the sender is not "self" 
then the extension will display 2 files with the same name but both will have 
the same new content.
        
        
        
2. Gmail File Space(GSpace) by Rahul Jonna 
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        - file injection. You can inject files into the "GSpace file system" by 
sending email with Subject: "GSPACE|new_filename.txt|2174|1|1|1|gs:/ d$" and 
putting "new_filename.txt" and "metadata.txt" as attachment. However the 
interface will fill the "from" information with the sender email address. The 
sender email address can be spoofed.
        
        - folder creation. You can create new folder by sending email with 
Subject: "GSPACE|test/|-135|1|1|0|gs:/ d$" and "blank.txt" and "metadata.txt" 
as attachment. However the interface will fill the "from" information with the 
sender email address. The sender email address can be spoofed.
        

Solution:
---------
  there are more possible solutions to filter unwanted content, such as 
inserting unpredictable id-s in the emails, message signing, but none (in my 
opinion) which can offer backward compatibility.