Date: Fri, 20 May 2005 19:17:10 +0200 From: Uwe Doering <gemini@geminix.org> To: Tim Traver <tt-list@simplenet.com> Cc: freebsd-security@freebsd.org Subject: Re: Possible PAWS security vulnerability Message-ID: <428E1B96.3020306@geminix.org> In-Reply-To: <428E0FD2.3070200@simplenet.com> References: <428E0FD2.3070200@simplenet.com>
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Tim Traver wrote: > Hello security gurus, > > yesterday, I mistakenly posted a question on the questions list about > this article : > > http://www.securityfocus.com/bid/13676/info/ > > which talks about a form of DOS vulnerability. > > I was curious as to the possibility of FreeBSD 5.x being affected, and > if anyone was working on this or not. > > Ted Mittelstaedt posted this possible patch based upon the OpenBSD patch : > > in /usr/src/sys/netinet > > *** tcp_input.c.original Thu May 19 11:52:30 2005 > --- tcp_input.c Thu May 19 12:00:14 2005 > *************** > *** 976,984 **** > --- 976,992 ---- > * record the timestamp. > * NOTE that the test is modified according to the latest > * proposal of the tcplw@cray.com list (Braden 1993/04/26). > + * NOTE2 additional check added as a result of PAWS > vulnerability > + * documented in Cisco security notice > cisco-sn-20050518-tcpts > + * from OpenBSD patch for OpenBSD 3.6 015_tcp.patch > */ > if ((to.to_flags & TOF_TS) != 0 && > SEQ_LEQ(th->th_seq, tp->last_ack_sent)) { > + if (SEQ_LEQ(tp->last_ack_sent, th->th_seq + tlen > + > + ((thflags & (TH_SYN|TH_FIN)) != 0))) > + tp->ts_recent = to.to_tsval; > + else > + tp->ts_recent = 0; > tp->ts_recent_age = ticks; > tp->ts_recent = to.to_tsval; > } I wonder, what good does it do to set 'tp->ts_recent' conditionally if you overwrite it with 'to.to_tsval' two lines later in any case. So far, I'd say this patch looks faulty. Apart from that, why develop your own patch when there is one already in CVS: http://www.freebsd.org/cgi/cvsweb.cgi/src/sys/netinet/tcp_input.c.diff?r1=1.252.2.15&r2=1.252.2.16&f=h As far as I can tell there are good chances that it even applies flawlessly to RELENG_4. Uwe -- Uwe Doering | EscapeBox - Managed On-Demand UNIX Servers gemini@geminix.org | http://www.escapebox.net
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