full-disclosure - RSA SecurID SID800 Token vulnerable by design

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Message-ID: <20060907184952.GA11869@danisch.de>
Date: Thu, 7 Sep 2006 20:49:52 +0200
From: hadmut@...isch.de (Hadmut Danisch)
To: full-disclosure@...ts.grok.org.uk, bugtraq@...urityfocus.com
Cc: 
Subject: RSA SecurID SID800 Token vulnerable by design

Hi,

I recently tested an RSA SecurID SID800 Token
http://www.rsasecurity.com/products/securid/datasheets/SID800_DS_0205.pdf

The token is bundled with some windows software designed to make
user's life easier. Interestingly, this software provides a function
which directly copies the current token code into the cut-and-paste
buffer, when the token is plugged in into USB. This is weak by design.

The security of these tokens is based on what RSA calls "two-factor
user authentication": It takes both a secret (PIN) and the
time-dependend Token-Code to authenticate. The security of the
Token-Code depends on the assumption that the token is resistant
against malware or intruders on the computer used for communication
(web browser, VPN client,...).

However, if the Token Code can be read over the USB bus, this
assumption does not hold. A single attack on the PC where the token is
plugged in would compromise both the PIN (e.g. with a keylogger) and
the token itself (e.g. writing a daemon which continuously polls the
token and forwards the token in real time to a remote attacker.

Ironically this could make an attack even easier: If some malware
simultaneously monitors the token and the keyboard, it is much easier
to detect that the keystrokes are actually related to some login
procedure:

Whenever the 6-digit token code appears in the keyboard or
cut-and-paste input stream, you can be pretty sure that in a sliding
window of about the last 100-200 keystrokes both the PIN and the
address of the server to login is contained. Makes it really easy to
automatically detect secrets in the input stream.

Thus, two different authentication methods are together weaker than
each single one.

regards
Hadmut

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