SNMP security issues in D-Link DSL Broadband Modem/Router

[Arhont Information Security <infosec () arhont com>]

Arhont Ltd      -       Information Security Company

Arhont Advisory by:             Andrei Mikhailovsky (www.arhont.com)
Advisory:                       D-Link DSL Broadband Modem/Router 
Router Model Name:              D-Link DSL-500
Model Specific:                 Other models might be vulnerable as well
Manufacturer site:              http://www.dlink.com
Manufacturer contact (UK):      Tel: 0800 9175063 / 0845
0800288         
Contact Date:                   06/03/2003

DETAILS:

While performing a general security testing of a
network, we have found several security vulnerability
issues with the D-Link DSL Broadband Modem DSL-500

Issue 1:
The default router installation enables SNMP (Simple
Network Management Protocol) server with default
community names for read and read/write access. The
DSL-500 modem is configured alow SNMP access from the
WAN (Wide Area Network)/Internet side as well as from LAN.

andrei@whale:~/bugtraq/DSL-modems$ snmpwalk -Os -c
public 192.168.0.1 -v 1
sysDescr.0 = STRING: D-Link DSL-500 version 7.1.0.30
Annex-A (Nov 28 2002) R2.21.002.04.b2t18uk
Copyright (c) 2000 Dlink Corp.
sysObjectID.0 = OID: enterprises.171.10.30.1
sysUpTime.0 = Timeticks: (14246347) 1 day, 15:34:23.47
...
...

The community name: public 

allows read access to the mentioned devices, allowing
enumeration and gathering of sensitive network
information.  

The community name: private 

allows read/write access to devices, thus allowing
change of the network settings of the broadband modem.

Impact: This vulnerability allows local and internet
malicious attackers to retrieve and change network
settings of the modem.

Risk Factor: Medium/High

Possible Solutions:  Firewall UDP port 161 from LAN/WAN
sides, as it is not possible to disable SNMP service
from the web management interface.

Issue 2:
The ISP account information including login name and
password is stored on the modem without encryption,  It
is therefore possible to retrieve this information with
simple SNMP gathering utility such as snmpwalk:

andrei@whale:~/bugtraq/DSL-modems$ snmpwalk -Os -c
public 192.168.0.1 -v 1
sysDescr.0 = STRING: D-Link DSL-500 version 7.1.0.30
Annex-A (Nov 28 2002) R2.21.002.04.b2t18uk
...
...
...
transmission.23.2.3.1.5.2.1 = STRING:
"username@dsl-provider"
...
...
transmission.23.2.3.1.6.2.1 = STRING: "password-string"
...
...
... 

Impact: This vulnerability allows LAN and internet
malicious attackers to retrieve confidential information.

Risk Factor: Very High

Possible Solutions:  As a temporary solution you should
firewall UDP port 161 from LAN/WAN sides, as it is not
possible to disable SNMP service from the web
management interface.

According to the Arhont Ltd. policy, all of the found
vulnerabilities and security issues will be reported to
the manufacturer 7 days before releasing them to the
public domains (such as CERT and BUGTRAQ), unless
specifically requested by the manufacturer.

If you would like to get more information about this
issue, please do not hesitate to contact Arhont team at
infosec () arhont com.


Kind Regards,

Andrei Mikhailovsky
Arhont Ltd
http://www.arhont.com
GnuPG Keyserver: blackhole.pca.dfn.de
GnuPG Key:       0xFF67A4F4