From: JC <bikkit@gmail.com>
To: Henrik Nordstrom <hno@marasystems.com>
Cc: Netfilter Developers <netfilter-devel@lists.netfilter.org>
Subject: Re: tcp match silently drops packets
Date: Mon, 17 Oct 2005 16:57:00 +0300 [thread overview]
Message-ID: <a60102c30510170657t7ecdaa9bk@mail.gmail.com> (raw)
In-Reply-To: <Pine.LNX.4.61.0510171549520.21372@filer.marasystems.com>
On 17/10/05, Henrik Nordstrom <hno@marasystems.com> wrote:
> On Mon, 17 Oct 2005, JC wrote:
>
> >> For the exact same reason the match also hotdrops fragments which would
> >> overwrite the TCP header.
> >>
> >> In theory just the second criteria is a must (drop fragments which could
> >> override an earlier decision), but as it's there the first also makes
> >> sense to drop the first as we can not allow a fragment filling in the
> >> missing pieces.
> >
> > Could someone please explain these two?
>
> An IP fragment with offset 1 can overwrite parts of the TCP header, and if
> this check is not there an attacker could bypass port matches in iptables
> by sending the packet in two fragments where the first fragment (which is
> used by the tcp match) has ports which is allowed by the ruleset and later
> the second fragment (which is ignored by the tcp match) overwrites the
> port numbers with ports which would not be allowed by the ruleset.
and that doesnt get picked up by conntrack as a different connection??
next prev parent reply other threads:[~2005-10-17 13:57 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-10-10 3:01 tcp match silently drops packets Philip Craig
2005-10-16 7:51 ` Yasuyuki KOZAKAI
2005-10-16 17:35 ` Henrik Nordstrom
2005-10-16 21:07 ` Henrik Nordstrom
2005-10-16 21:50 ` Herbert Xu
2005-10-17 19:30 ` Henrik Nordstrom
2005-10-17 21:27 ` Herbert Xu
2005-10-17 21:52 ` Henrik Nordstrom
2005-10-17 0:21 ` Philip Craig
2005-10-17 13:35 ` Henrik Nordstrom
2005-10-17 13:47 ` JC
2005-10-17 13:52 ` Henrik Nordstrom
2005-10-17 13:57 ` JC [this message]
2005-10-17 13:59 ` Henrik Nordstrom
2005-10-17 14:03 ` JC
2005-10-17 14:01 ` Cedric Blancher
2005-10-18 2:11 ` Herbert Xu
2005-10-18 8:31 ` Henrik Nordstrom
2005-10-17 0:18 ` Philip Craig
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