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           Louhi Networks Information Security Research
                        Security Advisory


     Advisory: A-Link WL54AP3 and WL54AP2 CSRF+XSS vulnerability
 Release Date: 2008/10/31
Last Modified: 2008/10/28
Authors: Jussi Vuokko, CISSP [jussi.vuokko@louhi.fi] 
Henri Lindberg [henri.lindberg@louhi.fi] 

       Device: A-Link WL54AP3 and WL54AP2 (any firmware)
     Severity: CSRF and XSS in management interface
         Risk: Moderate
Vendor Status: Vendor has released an updated version
References: http://www.louhinetworks.fi/advisory/alink_081028.txt 


Overview:

Quote from http://www.a-link.com/ 
   "WLAN Access point 54MB, 4-port
    Wlan Access point, wireless 54Mbps, DSSS, 802.11g-standard based and
    it's compatible also with other manufacturers cards."

   During an audit of A-Link WLAN54AP3 it was discovered that a cross
   site request forgery vulnerability exists in the management
   interface. It is possible for an attacker to perform any
   administrative actions in the management interface, if victim
   can be lured or forced to view malicious content. These administrative
   actions include e.g. changing admin user's username and password,
   DNS settings etc.

   In addition, it was discovered that no input validation or output
   encoding is performed in management interface, thus making it
   vulnerable to cross-site scripting.

   By default admin password is blank and no authentication is performed
   for requests to administrative interface. As ordinary consumers usually
   use out-of-the-box settings, this vulnerability offers same kind of
   phishing possibilities as used in Banamex attacks[1].

   A-Link WLAN54AP2 (EOL) is vulnerable to this threat as well.

[1] http://www.google.fi/search?q=banamex+phishing+dns+poison 


Details:

   A-Link WLAN54AP3 does not validate the origin of an HTTP request. If
   attacker is able to make user view malicious content, the WLAN54AP3
   device can be controlled by submitting suitable forms. Attacker is
   effectively acting as an administrator.

   Successful attack requires that the attacker knows the management
   interface address for the target device (default IP address is
   192.168.1.254). As the management interface does not have logout
   functionality, user can be vulnerable to this attack even after
   closing a tab containing the management interface (if user does not
   close the browser window or clear cookies and depending on browser
   behaviour) or if default blank password is used.


Proof of Concept:

   CSRF:

   Example form (changes DNS servers, enables WAN web server access
   and changes user's username and password):

   
   
action="http://192.168.1.254/goform/formWanTcpipSetup" 
    method="post" name="wan">
   
   
   
   
   
   
action="http://192.168.1.254/goform/formPasswordSetup" 
    method="post" name="password">
   
   
   
   
   
   

   XSS:

   Add following content to management interface's Management - DDNS -
   Domain Name:

"">src="http://l7.fi"> 


Workaround:

   -


Solution:

  Include a random user-specific token in forms. More information:
http://en.wikipedia.org/wiki/Cross-site_request_forgery 

  Perform an input validation and/or an output encoding. More information:
http://en.wikipedia.org/wiki/Cross_site_scripting 

  Use secure out-of-the-box configuration (for example generate
  default passwords based on device serial or MAC address using
  a secure cryptographic algorithm).


Disclosure Timeline:

   13. September 2008     - Contacted A-Link by email
   28. October 2008       - Vendor released an updated version
   31. October 2008       - Advisory was released


Copyright 2008 Louhi Networks Oy. All rights reserved.
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