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CERT Advisory CA-2001-08 Multiple Vulnerabilities in Alcatel ADSL Modems
Original release date: April 10, 2001
Last revised: --
Source: CERT/CC
A complete revision history can be found at the end of this file.
Systems Affected
* Alcatel Speed Touch Home ADSL Modem
* Alcatel 1000 ADSL Network Termination Device
Overview
The San Diego Supercomputer Center (SDSC) has recently discovered
several vulnerabilities in the Alcatel Speed Touch Asymmetric Digital
Subscriber Line (ADSL) modem. These vulnerabilities are the result of
weak authentication and access control policies and exploiting them
will lead to one or more of the following: unauthorized access,
unauthorized monitoring, information leakage, denial of service, and
permanent disability of affected devices.
The SDSC has published additional information regarding these
vulnerabilities at
http://security.sdsc.edu/self-help/alcatel/
I. Description
VU#211736 - Alcatel ADSL modems grant unauthenticated TFTP access via
Bounce Attacks
Alcatel ADSL modems allow unauthenticated Trivial File Transfer
Protocol (TFTP) access from the local area network (LAN) as a method
to update firmware and to make configuration changes to the device. In
conjunction with one of several common vulnerabilities, a remote
attacker may be able to gain unauthenticated access as well.
For example, if a system on the LAN side of the ADSL modem has the UDP
echo service enabled, a remote attacker may be able to spoof packets
such that the ADSL modem will believe that this traffic originated
from the local network. By sending a packet to the UDP echo service
with a spoofed source port of 69 (TFTP) and a source address of
255.255.255.255, the system providing the echo service can be tricked
into sending a TFTP packet to the ADSL modem. If a system offering
this service is accessible from the Internet it may be possible to use
the system to attack the ADSL modem.
Any mechanism for "bouncing" UDP packets off systems on the LAN side
of the network may potentially allow a remote attacker to gain TFTP
access to the device. Gaining TFTP access to the device allows the
remote attacker to essentially gain complete control of the device.
VU#243592 - Alcatel ADSL modems provide EXPERT administrative account
with an easily reversible encrypted password
Alcatel ADSL modems contain a special account (EXPERT) for gaining
privileged access to the device. This account is secured via a
challenge-response password authentication mechanism. While the use of
such a mechanism is commendable, the algorithm used is not
sufficiently strong. Attackers who know the algorithm used to compute
the response can compute the correct response using information given
to them during the login process.
Because the EXPERT account is accessible via TELNET, HTTP, and FTP,
the ADSL modem must have an IP address that is accessible from the
Internet to exploit this vulnerability. Alcatel ADSL products do not
enable this feature over the wide area network (WAN) interface by
default. Note however, that an attacker with TFTP access may be able
to reconfigure the device to enable this feature.
This authentication mechanism is present even if the user has set a
user supplied password.
Any problem or vulnerability on your internal network that allows an
intruder to communicate with the modem may lead to its compromise,
including Trojan horses, compromised systems, or other "bounce"
vulnerabilities like the FTP bounce vulnerability described in
http://www.cert.org/tech_tips/ftp_port_attacks.html
VU#212088 - Alcatel ADSL modems contain a null default password
The Alcatel Speed Touch ADSL modem ships with a null default password,
permitting unauthenticated access via TELNET, HTTP, and FTP. As with
the EXPERT account vulnerability, the device must have an externally
accessible IP address.
VU#490344 - Alcatel ADSL modems provide unauthenticated TFTP access
via physical access to the WAN interface
To allow your ISP to upgrade the firmware of the ADSL modem remotely,
unauthenticated TFTP access is provided to users with physical access
to the wire on the WAN side of the modem. While this access is
normally used by your ISP, it could also be abused by an attacker with
physical access to the wire outside of your home.
II. Impact
VU#211736 - Alcatel ADSL modems grant unauthenticated TFTP access via
Bounce Attacks
A remote attacker may be able to gain access to perform TFTP
operations. These operations include
* inspection of configuration data
* recovery and setting of passwords
* inspection and updates to the firmware
* destructive updates to the firmware
* malicious custom updates to the firmware
Note that the Alcatel ADSL modems do not provide any mechanism for
determining the validity of firmware updates, so a remote attacker may
be able to install custom firmware that operated as a distributed
denial of service client or a network sniffer. Similarly, an attacker
could produce an invalid firmware revision that would disable the
device completely, leaving victims no alternative but to return the
disabled unit to the manufacturer.
VU#243592 - Alcatel ADSL modems provide EXPERT administrative account
with an easily reversible encrypted password
Attackers who are able to connect to the ADSL modem can enter a
predictable user ID and password to gain privileged access to the
device. This access can be used to reconfigure the device, potentially
introducing additional security weaknesses.
VU#212088 - Alcatel ADSL modems contain a null default password
Unless the user or Internet service provider changes the default
password of an affected device, a remote attacker can access the modem
via TELNET, HTTP, or FTP. In the case of TELNET and HTTP, this
vulnerability grants the attacker read and write access to device
configuration. For FTP, this vulnerability allows the attacker to
browse the file structure of the affected device.
VU#490344 - Alcatel ADSL modems provide unauthenticated TFTP access
via physical access to the WAN interface
An attacker with physical access to your wire may be able to gain
unauthenticated TFTP access to the device with the same impacts as
described in the "bounce" vulnerability (VU#211736).
III. Solution
Set a password for your ADSL modem
Because the Alcatel ADSL modems ship without a password by
default, an attacker may be able to gain access if this
password has not been set. Users are encouraged to set a
password when the device is first configured. This solution
does not protect you from all of the vulnerabilities described
above. In particular, a user supplied password does not prevent
the use of the EXPERT account.
Block malicious traffic at your network perimeter
If you have a home firewall product you may be able to prevent
the TFTP UDP bounce attack by filtering one or more of the
following types of traffic:
+ packets with spoofed source addresses
+ packets with a source address of 255.255.255.255
+ packets with a destination port of echo (or other "simple"
services)
Note that intruders who are able to gain access to your local
area network may be able to gain unauthenticated TFTP access
using mechanisms other than the TFTP UDP bounce method.
Appendix A. - Vendor Information
This appendix contains information provided by vendors for this
advisory. When vendors report new information to the CERT/CC, we
update this section and note the changes in our revision history. If a
particular vendor is not listed below, we have not received their
comments.
Alcatel
ALCATEL SPEED TOUCH ADSL MODEM SECURITY INFORMATION
About security of Modems and Networks
Security issues can be divided into two main areas: network
security and user security, more particularly user's content
security.
Wide Area Network (WAN) security is about protecting a network
from malicious usage. Security can be guaranteed at all network
levels except at Customer Premise Equipment (CPE), since such
equipment is not directly controlled by an Operator or an ISP.
This is true for any type of CPE, such as telephones, analogue,
DSL or cable modems and fax machines. Security can only be
guaranteed at the network level for an Operator's, ISP's or
private network. This means that a network should stay
operational at all times. Alcatel has built this type of
security in its DSLAM (operated by the service provider).
User security is about protecting the content and local area
network of an end-user. This type of security has to be
implemented on Local Area Network (LAN) or PC level at customer
premises.
This is standard practice for any network connection (leased
lines, cable modem, DSL). Such modems provide connectivity not
security. Security of content for the user can be reinforced at
the LAN level by installing a dedicated firewall HW/SW, either
on the server or on the PC or by installing a dedicated
firewall device, although Alcatel provides also DSL modems
which have firewall security Statement. Private and LAN
security is in the responsibility of the user.
There are many soft and hardware products on the market to
ensure security, including those from Alcatel.
Modem security
Firstly, people have been able to alter firmware on the modem.
This is a standard feature foreseen in some of the Speed Touch
modems to allow SW upgrades locally or remotely. Access from
the LAN interface into the modem is not a security problem,
since the modem belongs to the person who is using it. However,
via a protection mechanism a feature is foreseen so that nobody
can do that remotely (or via the WAN/DSL interface). This
protection mechanism guarantees that nobody from outside can
access the modem and make changes.
This protection can be switched off locally by the modem owner,
in case the service provider wants to do upgrades. This process
is normally managed by the service provider, and the service
provider explains to the end-user how to disactivate the
protection and re-activate again. To avoid security problems,
this feature is not explained in the user manual.
Alcatel ships all modems with the protection activated,
however, it's easy for a modem owner to disactivate the
protection, since this is documented on the Alcatel website.
However, if a user disactivates this, he's also responsible for
activating it again.
Secondly, the method of getting into the modem is more advanced
and it is a standard practice used by hackers. The way it works
is that they fake local communication via the WAN interface by
using an ECHO port on a UNIX server connected to LAN network.
The modem assumes communication comes from the modem owner and
is secure. However, this is an old security problem in all data
communication networks and is solved by means of a firewall.
Firewall's are standard practice for each well managed
communication network. Recommendation that Alcatel gives is to
install a dedicated firewall or firewall software, or make use
of the Alcatel Speed Touch modem with Firewall capabilities.
(See URL: http://www.alcatel.com/consumer/dsl/prodprofw.htm)
_________________________________________________________________
The CERT Coordination Center would like to thank Tom Perrine and
Tsutomu Shimomura of the San Diego Supercomputer Center for notifying
us about this problem and their help in constructing this advisory.
_________________________________________________________________
Authors: This document is based on research by the SDSC and was
written by Cory Cohen, Jeffrey P. Lanza, and John Shaffer.
______________________________________________________________________
This document is available from:
http://www.cert.org/advisories/CA-2001-08.html
______________________________________________________________________
CERT/CC Contact Information
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Phone: +1 412-268-7090 (24-hour hotline)
Fax: +1 412-268-6989
Postal address:
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Revision History
April 10, 2001: Initial release
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