vuln.sg Vulnerability Research Advisory

AceFTP FTP-Client Directory Traversal Vulnerability

by Tan Chew Keong
Release Date: 2008-06-27

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Summary

A vulnerability has been found within the FTP client in AceFTP. When exploited, this vulnerability allows an anonymous attacker to write files to arbitrary locations on a Windows user's system.


Tested Versions


Details

This advisory discloses a vulnerability within the FTP client in AceFTP. When exploited, this vulnerability allows an anonymous attacker to write files to arbitrary locations on a Windows user's system.

The FTP client does not properly sanitise filenames containing directory traversal sequences (forward-slash) that are received from an FTP server in response to the LIST command.

An example of such a response from a malicious FTP server is shown below.


Response to LIST (forward-slash):

-rw-r--r--    1 ftp      ftp            20 Mar 01 05:37 /../../../../../../../../../testfile.txt\r\n
 

By tricking a user to download a directory from a malicious FTP server that contains files with fowward-slash directory traversal sequences in their filenames, it is possible for the attacker to write files to arbitrary locations on a user's system with privileges of that user. An attacker can potentially leverage this issue to write files into a user's Windows Startup folder and execute arbitrary code when the user logs on.


POC / Test Code

Please download the POC here and follow the instructions below.

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Patch / Workaround

Avoid downloading files/directories from untrusted FTP servers.


Disclosure Timeline

2008-06-15 - Vulnerability Discovered.
2008-06-16 - Vulnerability Details Sent to Vendor via online support form (no reply).
2008-06-18 - Vulnerability Details Sent to Vendor again via online support form (no reply).
2008-06-25 - Vulnerability Details Sent to Vendor again via online support form (no reply).
2008-06-27 - Public Release.


Contact
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