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.
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	- folder creation. You can create new folder by sending email with Subject: "GMAILFS: /new_folder/. [14;a;1]"
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	- 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.
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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$" and putting "new_filename.txt" and "metadata.txt" as attachment. However the interface will fill the "from" information with the sender email address. The sender email address can be spoofed.
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	- folder creation. You can create new folder by sending email with Subject: "GSPACE|test/|-135|1|1|0|gs:/ d$" 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.
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Solution:
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  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.