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Linksys WRT54GS WPA Personal/TKIP Authentication Flaws
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SUMMARY
Linksys WRT54GS is "Internet-sharing Router, 4-port Switch, and
performance enhanced Wireless-G (802.11g) Access Point". A flaw in Linksys
WRT54GS Wireless Router allows unauthorized access when WPA/TKIP
authentication mode is on.
DETAILS
Vulnerable Systems:
* Linksys WRT54GS firmware version 4.50.6
It appears that firmware version 4.50.6 for the Linksys WRT54GS (hardware
version 1) wireless router allows wireless clients to connect and use the
network without actually authenticating. With
<http://en.wikipedia.org/wiki/Wi-Fi_Protected_Access> WPA Personal/
<http://en.wikipedia.org/wiki/TKIP> TKIP authentication enabled, the unit
allows both clients using encryption with the correct settings and key,
and clients not using any encryption. It disallows clients attempting to
use encryption with the wrong settings and/or key.
In other words, even if you think you've secured your wireless network
from unauthorized access, anyone can access it. It actually shows up as
having no password security on a Macstumbler scan, which is how the
problem noticed. It was verified that anyone can access the network
without needing to know the key.
No security modes other than WPA/TKIP were checked. Other modes may have
different behavior. Changing the "Authentication Type" setting had no
effect on this problem. Its believed it should be set to "Shared Key", but
the setting used does not appear to matter.
The problem was verified only on firmware 4.50.6. It is unknown if other
firmware versions exhibit the problem. However, at least one older
firmware does not exhibit the problem, as router functioned correctly
until updated to 4.50.6.
The problem appears to be fixed in version 4.70.6. No explicit notice of
this problem or the fix appears in the release notes for version 4.70.6.
Strangely, the "Authentication Type" must be set to "Auto" for the unit to
function properly. Should it be set to "Shared Key", which one might
expect to be the correct value, the wireless functionality appears to be
entirely disabled.
It is unknown if this problem is seen with other hardware versions, or
with other models. Its suspected it may, given the similarity between many
of the Linksys models and their firmware.
ADDITIONAL INFORMATION
The information has been provided by <mailto:bugtraq@moonsoft.com> Steve
Scherf.
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