dlink614.txt

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TITLE: Security flaw in DLINK 614+ - SOHO routers (http://www.dlink.com)  
  
TYPE: Script injection over DHCP  
  
QUOTE from DLINK:  
  
The AirPlus DI-614+ combines the latest advancements in 802.11b  
silicon chip  
design from Texas Instruments, utilizing their patented Digital Signal  
ProcessingTM technology, and D-Link?s own robust firewall security  
features.  
...  
A simple yet intelligent, web-based setup wizard makes the DI-614+  
easy for any  
user to quickly and securely connect computers to share a high-speed  
Internet  
connection, files, resources, games or just to communicate. An  
integrated 4-port  
switch allows direct connection of up to four computers. Several wireless  
clients can also securely connect to the network using 64, 128, or  
256-bit  
encryption.  
...  
The D-Link AirPlus DI-614+ is the ideal networking solution for small  
offices,  
home offices, schools, coffee shops and other small businesses that  
cater to the  
public.  
  
  
  
DETAILS:  
  
  
The DI-614+ SOHO router (latest firmware rev 2.30) suffers a "script  
injection over dhcp" vulnerability.  
Using DHCP as a vector, arbitrary and malicious scripting can be  
injected into the DHCP administrative and logs pages (if enabled)  
  
Scripting sent in such a way will be executed on behalf of the unaware  
administrator when he consult the web based management interface and  
lead to the complete compromising of the  
firewall/router giving full access to the administrative account.  
  
The DI-614+ does not filter user supplied data passed through the DHCP  
HOSTNAME option.  
Basically, it first truncates the string to 20 characters and displays  
it AS IS in the DHCP and log pages  
opening a large hole that can easily be exploited for instance:  
to change the administrator password (doesn't require his current  
password), to reboot the box, to reset the box's factory settings.  
  
Because the DLINK 614+ is used, among others, by coffee shops, a  
successful exploitation may have very serious impact.  
  
  
EXPLOITATION:  
  
As an example, one can inject a script designed to force the  
administrator into restoring the box default settings  
using this nasty little script:  
  
<iframe height=0 width=0 src='restore.cgi'>  
  
where a call to restore.cgi indeed restore the box factory defaults.  
  
problem #1:  
  
the DI-614+ will truncate this code into:  
  
<iframe height=0 wid ** CGI ADDED STUFF **  
  
20 characters is obviously not enough to do something useful here.  
Splitting this script into 3 parts, sending each of them in a  
different DHCPREQUEST along  
with a different CLIENTID option or Mac address will create 3 new  
differents entries in the DHCP admin page.  
something like:  
  
<iframe height=0 wid** CGI ADDED STUFF **  
th=0 src='restore.cgi'** CGI ADDED STUFF **  
| ** CGI ADDED STUFF **  
  
problem #2:  
  
the result is still bogus from a browser perspective, because of the  
other tags (noted above as CGI ADDED STUFF) inserted between  
each new entry.  
However a dirty trick allows to circumvent this problem by finishing  
each fragment with an id option and doing so, quoting the ** CGI added  
stuff **.  
like this (this time in four packets):  
  
<iframe id='**CGI ADDED STUFF**  
' height=0 id='**CGI ADDED STUFF**  
' width=0 id='**CGI ADDED STUFF**  
' src='restore.cgi'>  
  
Result is quite awful for a human but also readable for most browsers,  
afterwhat, next time the site administrator opens the DHCP page,  
he will automaticaly, and without notice, restores the box default  
password (blank), disable wireless encryption, etc...  
Finally X has to connect to 192.168.0.1 (default address), and voila !  
he is administrator.  
  
This vulnerability can be exploited from both wire and wireless networks.  
The solution is simply to filter the HOSTNAME DHCP option supplied by  
users by escaping html meta-characters  
  
  
  
VENDOR:  
  
DLINK's support staff has been contacted by May 24th but didn't reply  
to my questions  
No idea if a new firmware will be made available soon and even if they  
are currently working on it  
It looks like they just don't care too much about security.  
  
  
WORKAROUND:  
Use static leasing only (it fixes the hostname) otherwise just use a  
real dhcpd daemon (and disable DLINK dhcpd)  
  
  
VULNERABLE:  
  
firmware up to rev 2.30 (latest)  
  
  
  
AUTHOR: Gregory Duchemin (c3rb3r at sympatico.ca)  
  
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