AusCERT - ESB-2004.0504 -- iDEFENSE Security Advisory 08.05.04 -- Thompson SpeedTouch Home ADSL Modem Predictable TCP ISN Generation

HOME
About AusCERT
Membership
PKI Services
Training
Publications
Sec. Bulletins
Conferences
News & Media
Services
Web Log
Site Map
Site Help
Member login
ESB-2004.0504 -- iDEFENSE Security Advisory 08.05.04 -- Thompson SpeedTouch Home ADSL Modem Predictable TCP ISN Generation
Date: 10 August 2004

Click here for printable version
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

===========================================================================
             AUSCERT External Security Bulletin Redistribution

           ESB-2004.0504 -- iDEFENSE Security Advisory 08.05.04
    Thompson SpeedTouch Home ADSL Modem Predictable TCP ISN Generation
                              10 August 2004

===========================================================================

        AusCERT Security Bulletin Summary
        ---------------------------------

Product:                Thompson (formerly Alcatel) SpeedTouch ADSL router
Publisher:              iDEFENSE
Impact:                 Reduced Security
Access:                 Remote/Unauthenticated
CVE Names:              CAN-2004-0641

- --------------------------BEGIN INCLUDED TEXT--------------------

Thompson SpeedTouch Home ADSL Modem Predictable TCP ISN Generation

iDEFENSE Security Advisory 08.05.04:

I. BACKGROUND

The Thompson (formerly Alcatel) SpeedTouch is an ADSL router for home
and business providing a continuously available, "always on,"
connection. More information about the product can be found at
http://www.speedtouchdsl.com/.

II. DESCRIPTION

Remote exploitation of a design error vulnerability in Thompson's
SpeedTouch Home ADSL modem allows attackers to spoof TCP traffic on
behalf of the device.

The problem specifically exists due to the predictable nature of the TCP
Initial Sequence Number (ISN) generator on the device. The following
sanitized tcpdump output demonstrates the existence of the vulnerability
when 10 consecutive TCP connection requests are generated for the telnet
server (port 23) on the Thompson device:

48.3 host_a.1096   > host_b.telnet: S
48.3 host_b.telnet > host_a.1096: S 4081040897:4081040897(0) ack
48.3 host_a.1096   > host_b.telnet: R
48.4 host_a.1096   > host_b.telnet: S
48.4 host_b.telnet > host_a.1096: S 4081104897:4081104897(0) ack
48.4 host_a.1096   > host_b.telnet: R
48.6 host_a.1096   > host_b.telnet: S
48.6 host_b.telnet > host_a.1096: S 4081232897:4081232897(0) ack
48.6 host_a.1096   > host_b.telnet: R
48.7 host_a.1096   > host_b.telnet: S
48.7 host_b.telnet > host_a.1096: S 4081296897:4081296897(0) ack
48.7 host_a.1096   > host_b.telnet: R
48.9 host_a.1096   > host_b.telnet: S
48.9 host_b.telnet > host_a.1096: S 4081360897:4081360897(0) ack
48.9 host_a.1096   > host_b.telnet: R
49.0 host_a.1096   > host_b.telnet: S
49.0 host_b.telnet > host_a.1096: S 4081488897:4081488897(0) ack
49.0 host_a.1096   > host_b.telnet: R
49.2 host_a.1096   > host_b.telnet: S
49.2 host_b.telnet > host_a.1096: S 4081552897:4081552897(0) ack
49.2 host_a.1096   > host_b.telnet: R
49.3 host_a.1096   > host_b.telnet: S
49.3 host_b.telnet > host_a.1096: S 4081616897:4081616897(0) ack
49.3 host_a.1096   > host_b.telnet: R
49.5 host_a.1096   > host_b.telnet: S
49.5 host_b.telnet > host_a.1096: S 4081744897:4081744897(0) ack
49.5 host_a.1096   > host_b.telnet: R
49.6 host_a.1096   > host_b.telnet: S
49.6 host_b.telnet > host_a.1096: S 4081808897:4081808897(0) ack
49.6 host_a.1096   > host_b.telnet: R

In the above example, host_a is the querying host and host_b is the
Thompson device. A clear pattern in ISN generation can be seen as the
value increases by approximately 64,000 each millisecond.

III. ANALYSIS

Successful exploitation of weak ISNs for the purpose of connection
spoofing is not a trivial task. Successful exploitation allows an
attacker to generate traffic on behalf of the affected device. Such an
ability is most dangerous when trust paths exist between the affected
device and another remote system.

IV. DETECTION

iDEFENSE has verified the existence of this vulnerability in Thompson's
SpeedTouch firmware version GV8BAA3.270 (1003825). It is suspected that
earlier versions are susceptible to exploitation as well.

V. WORKAROUNDS

Untrusted traffic should be filtered at the network perimeter.

VI. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2004-0641 to this issue. This is a candidate for inclusion in
the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

VII. DISCLOSURE TIMELINE

06/08/04   Initial vendor contact - no response
06/08/04   iDEFENSE clients notified
06/18/04   Secondary vendor contact - no response
08/05/04   Public disclosure

VIII. CREDIT

The discoverer wishes to remain anonymous.

Get paid for vulnerability research
http://www.idefense.com/poi/teams/vcp.jsp

IX. LEGAL NOTICES

Copyright © 2004 iDEFENSE, Inc.

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
written consent of iDEFENSE. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically, please
email customerservice@idefense.com for permission.

Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.

- --------------------------END INCLUDED TEXT--------------------

You have received this e-mail bulletin as a result of your organisation's
registration with AusCERT. The mailing list you are subscribed to is
maintained within your organisation, so if you do not wish to continue
receiving these bulletins you should contact your local IT manager. If
you do not know who that is, please send an email to auscert@auscert.org.au
and we will forward your request to the appropriate person.

NOTE: Third Party Rights
This security bulletin is provided as a service to AusCERT's members.  As
AusCERT did not write the document quoted above, AusCERT has had no control
over its content. The decision to follow or act on information or advice
contained in this security bulletin is the responsibility of each user or
organisation, and should be considered in accordance with your organisation's
site policies and procedures. AusCERT takes no responsibility for consequences
which may arise from following or acting on information or advice contained in
this security bulletin.

NOTE: This is only the original release of the security bulletin.  It may
not be updated when updates to the original are made.  If downloading at
a later date, it is recommended that the bulletin is retrieved directly
from the author's website to ensure that the information is still current.

Contact information for the authors of the original document is included
in the Security Bulletin above.  If you have any questions or need further
information, please contact them directly.

Previous advisories and external security bulletins can be retrieved from:

        http://www.auscert.org.au/render.html?cid=1980

If you believe that your computer system has been compromised or attacked in 
any way, we encourage you to let us know by completing the secure National IT 
Incident Reporting Form at:

        http://www.auscert.org.au/render.html?it=3192

===========================================================================
Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072

Internet Email: auscert@auscert.org.au
Facsimile:      (07) 3365 7031
Telephone:      (07) 3365 4417 (International: +61 7 3365 4417)
                AusCERT personnel answer during Queensland business hours
                which are GMT+10:00 (AEST).
                On call after hours for member emergencies only.
===========================================================================

-----BEGIN PGP SIGNATURE-----
Comment: http://www.auscert.org.au/render.html?it=1967

iQCVAwUBQRiBbSh9+71yA2DNAQKvMwP9EKWXSQSZj5GaQusdCkWehHEOr/WqXtt0
j9NHGJkkI760FnWc4+ja1S995Oly8TUyhsQq7CL+CcfzUW2snBpXzl2OMBMEkLGw
GXdDzlim68XGysvkrmEtJ+jgS1lqSiBFKhWzmwmB5Wxby22HCt8+9/gv3MUSOEPR
Hkz2yZMlGLI=
=o2NO
-----END PGP SIGNATURE-----