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From: guninski at guninski.com (Georgi Guninski)
Subject: Remote openbsd crash with ip6, yet still openbsd much better than windows

Georgi Guninski security advisory #66, 2004

Remote openbsd crash with ip6, yet still openbsd much better than windows

Systems affected:
tested on openbsd 3.4
not clear about netbsd
freebsd not vulnerable

Risk: Medium
Date: 4 February 2004

Legal Notice:
This Advisory is Copyright (c) 2004 Georgi Guninski.
You may distribute it unmodified.
You may not modify it and distribute it or distribute parts
of it without the author's written permission - this especially applies to
so called "vulnerabilities databases" and securityfocus, microsoft, cert
and mitre.
If you want to link to this content use the URL:
http://www.guninski.com/obsdmtu.html
Anything in this document may change without notice.

Disclaimer:
The information in this advisory is believed to be true though
it may be false.
The opinions expressed in this advisory and program are my own and
not of any company. The usual standard disclaimer applies,
especially the fact that Georgi Guninski is not liable for any damages
caused by direct or  indirect use of the information or functionality
provided by this advisory or program. Georgi Guninski bears no
responsibility for content or misuse of this advisory or program or
any derivatives thereof.

Description:
It is possible to remotely crash openbsd 3.4 if the host receives icmpv6
and there is a listening tcp port.
quoting de raadt: "it is just a crash."
remote crash which screws the kernel.
unknown whether this may be exploited for code execution.

Details:
The problem is triggered by setting small ipv6 mtu and then doing tcp
connect.
How to reproduce:
Patch linux kernel 2.4.24 net/ipv6/icmp.c :
case ICMPV6_ECHO_REPLY:
		/* we coulnd't care less */
icmpv6_send(skb, ICMPV6_PKT_TOOBIG, 0, 68, skb->dev); //joro

ping6 openbsd
ssh -6 openbsd

Workaround:
It is believed that openbsd current is not vulnerable.
netbsd current also seems to have related changes.
check:
http://www.openbsd.org/cgi-bin/cvsweb/src/sys/netinet6/ip6_output.c
http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/netinet/tcp_output.c?sortby=date

Vendor status:
open, net and freebsd were notified Sun, 1 Feb 2004 16:35:56 +0200

Georgi Guninski
http://www.guninski.com




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