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Re: IGMP denial of service vulnerability
From: Marty Schoch <mschoch () multicasttech com>
Date: 14 Jun 2002 14:45:33 -0400


Solution
---------
All IGMP packets that are not multicast ethernet addresses should be 
dropped.

Depending on the implementation of router R in linked document, couldn't
there still be a problem in the following scenario.

Host H1 is a member of two groups 230.0.0.1 and 230.0.0.2
Host H2 sends a membership report for group 230.0.0.1 to group
230.0.0.2.

Host H1 will obviously see this report as well.
Looking briefly at the code it appears host H1 may still consider this
an acceptable report from another host.  If, and I haven't tested any
router configurations, router R does not consider this a valid report
for the group 230.0.0.1 then the same DOS effect may occur.

The RFC says that membership reports should be sent to the group for
which the report applies.  Why not tighten the code down all the way, to
check not just that the report is multicast, but that all the addresses
match.

Marty Schoch
<mschoch () multicasttech com>


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