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WEP-Client-Communication-Dumbdown (WCCD) Vulnerability (re-send)
From: "security () hammerjammer net" <security () hammerjammer net>
Date: Tue, 17 Jan 2006 10:51:33 +0800
sorry, earlier email seems to have not gotten through....
------- Forwarded message follows -------
To: full-disclosure () lists grok org uk
Subject: WEP-Client-Communication-Dumbdown (WCCD) Vulnerability
Date sent: Mon, 16 Jan 2006 17:23:09 +0800
ThinkSECURE Pte Ltd (www.securitystartshere.net) has released
details of a client-side wireless vulnerability which affects
wireless users who are still using WEP.
More details including mitigation actions are available at our
### Vulnerability Name ###
WEP-Client-Communication-Dumbdown (WCCD) Vulnerability
### Vulnerability Description ###
ThinkSECURE has discovered that certain well-known wireless chipsets,
using vulnerable drivers under the Windows XP operating system and
when configured to use WEP with Open Authentication, can be tricked
by a 802.11-based wireless client adapter operating in master mode
("the attacker") to discard the WEP settings and negotiate a post-
association conection with the attacker in the clear.
We have named this vulnerability as the "WEP-client-communication-
dumbdown" (wccd) vulnerability.
This vulnerability is apparently not due to Windows itself but due to
the operation of the drivers for the affected wireless cards.
However, this does not discount a situation where a patch could be
released by Microsoft to deal with the problem on the chipset makers'
Again, this is apparently NOT a Windows problem but a wireless
chipset driver-related one.
End-users of the system would not notice any difference about the
clear connection that was being established.
Although WPA/2 & WPA-PSK have been out for some time now, in our
experience there is still a large installed client base who are still
using WEP-enabled Access Points and thus have WEP-enabled profiles
setup in their laptops. This installed base is vulnerable.
### Vulnerability Impact ###
The vulnerability was observed in a Windows XP wireless client
configuration with the vulnerable drivers and with the following
1. Profile configured using Windows XP zero configuration as well as
using the vulnerable drivers' bundled wireless client managers;
2. Profile configured to use WEP with static WEP key & Open
Using ThinkSECURE's recently-released security auditor's tool -
probemapper - one can remotely evaluate the SSID and capabilities of
wireless profiles from probe requests and assess whether the subject
is probing for any Open-Authentication-WEP-encryption-enabled
When a Windows XP client using a vulnerable chipset driver is
configured as outlined above via their wireless profiles ("the
victim"), the victim will send out probe requests bearing the SSID
configured in the wireless profile.
An attacker who detects the probe request frames coming from the
configured profile can configure a master-mode-enabled wireless card
with the detected SSID of the probe request frames and, using Open
Authentication with no-encryption, send probe responses to the
The victim will then initiate authentication and association, sending
an association request frame with the Privacy Bit set to 1 (AP/STA
can support WEP).
The attacker returns an association response frame with Privacy Bit
set to 0 (AP/STA cannot support WEP).
Although the correct behavior should be to not establish any
communication due to the difference between association request and
response Privacy Bits, the victim "dumbs-down" and establishes an un-
encrypted communications session to match the attacker's Privacy Bit
setting of 0, thus ignoring the WEP settings as configured in the
client's profile. All traffic to & from this connection will be sent
in the clear.
A victim who has a vulnerable wireless network at home and brings a
laptop bearing the profile of said home wireless network to his/her
organization and plugs in using a wired connection may be attacked in
this manner and used as a conduit by the attacker, through the
bridging of the laptop's wireless interface to the wired interface,
to the victim's organization's wired network, thus bypassing
corporate perimeter defences. It is irrelevant that the organization
does not use wireless or has a no-wireless policy if that policy is
not strictly enforced through proactive checking.
Also, firewalling on the victim's laptop might not guarantee safety
in certain cases: e.g. the attacker issues an IP address and gateway
address to the victim in response to the victim's typical DHCP
request upon association so as to fool the victim's machine into
forwarding all traffic to the attacker's machine. The result is that,
when the victim opens up a web browser for example, he will see a
crafted page bearing malicious code on the attacker's machine which
runs exploit code on the victim's machine (a good example being the
recent WMF vulnerability) to give the attacker a reverse shell into
the victim, where the attacker can then do the bridging of the
interface or anything else he wants.
### Vulnerability Cause ###
In our testing, we have narrowed down the cause of the problem to
stem from the way certain chipset manufacturer drivers deployed for
the Windows platform operate in handling an association.
Affected chipset manufacturer(s) have been notified via their website
In the interests of responsible disclosure, we will not be stating
which chipset drivers which we tested as vulnerable for a minimum
period of 14 days after this vulnerability advisory, thus giving time
for the notified vendors to issue non-vulnerable drivers. (dated 16
### Vulnerability Discovery Acknowledgment ###
Christopher Low & Julian Ho of ThinkSECURE Pte Ltd
(http://www.securitystartshere.net) discovered and researched this
vulnerability from Dec 2005 to 15 Jan 2006.
------- End of forwarded message -------
Full-Disclosure - We believe in it.
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- WEP-Client-Communication-Dumbdown (WCCD) Vulnerability (re-send) security () hammerjammer net (Jan 17)