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AUSCERT External Security Bulletin Redistribution
ESB-2020.0898
NetBSD Security Advisory 2020-002: Specific ICMPv6 error
message packet can crash the system
12 March 2020
===========================================================================
AusCERT Security Bulletin Summary
---------------------------------
Product: kernel
Publisher: NetBSD
Operating System: NetBSD
Impact/Access: Denial of Service -- Remote/Unauthenticated
Resolution: Patch/Upgrade
Original Bulletin:
https://ftp.netbsd.org/pub/NetBSD/security/advisories/NetBSD-SA2020-002.txt.asc
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NetBSD Security Advisory 2020-002
=================================
Topic: Specific ICMPv6 error message packet can crash the system
Version: NetBSD-current: affected untill January 23, 2020
NetBSD 9.0: not affected
NetBSD 8.1: affected
NetBSD 7.x: not affected
Severity: Remote packets can crash the machine
Fixed: NetBSD-current: January 23, 2020
NetBSD-9 branch: January 23, 2020
NetBSD-8 branch: January 23, 2020
NetBSD-7 branch: not affected
Please note that NetBSD releases prior to 7.1 are no longer supported.
It is recommended that all users upgrade to a supported release.
Abstract
========
Due to a mistake in IP-IP tunnel packet processing, a malicious ICMPv6
error message packet whose payload is an IP-IP tunnel packet
can cause incorrect resource freeing leading to a system crash.
This is a remote DoS, that affects all systems that have IPv6 enabled.
Technical Details
=================
NetBSD-7 is not affected since it does not use the resource that
is erroneously being freed.
Solutions and Workarounds
=========================
1. Filter out ICMPv6 'packet too big'-type packets using NPF. Here's an
example npf.conf file, assuming wm0 is the interface to be protected:
$int_if = ifaddrs(wm0)
group default {
block in final on $int_if family inet6 proto ipv6-icmp icmp-type 2 all
pass in on $int_if all
pass out on $int_if all
}
Note that this workaround disables reception of packet-too-big icmp6 messages
which are necessary for the host to perform pmtu discovery.
If a remote host is on a network with a smaller MTU, IPv6 communication may
not work properly.
2. Update the kernel to a fixed version and reboot.
To apply a fixed version from a releng build, fetch a fitting kern-GENERIC.tgz
from nyftp.netbsd.org and extract the fixed binaries:
cd /var/tmp
ftp https://nycdn.NetBSD.org/pub/NetBSD-daily/REL/latest/ARCH/binary/sets/kern-GENERIC.tgz
cd /
tar xzpf /var/tmp/kern-GENERIC.tgz
with the following replacements:
REL = the release version you are using
ARCH = your system's architecture
The following instructions describe how to upgrade your kernel by
updating your source tree and rebuilding and installing a new version.
For all NetBSD versions, you need to obtain fixed kernel sources,
rebuild and install the new kernel, and reboot the system.
The fixed source may be obtained from the NetBSD CVS repository.
The following instructions briefly summarise how to upgrade your
kernel. In these instructions, replace:
ARCH with your architecture (from uname -m), and
KERNCONF with the name of your kernel configuration file.
To update from CVS, re-build, and re-install the kernel:
# cd src
# cvs update -d -P src/sys/netinet/ip_encap.c
# ./build.sh kernel=KERNCONF
# mv /netbsd /netbsd.old
# cp sys/arch/ARCH/compile/obj/KERNCONF/netbsd /netbsd
# shutdown -r now
For more information on how to do this, see:
http://www.NetBSD.org/docs/guide/en/chap-kernel.html
The patches can be obtained from NetBSD-current with the following
command:
cvs rdiff -u -r1.71 -r1.72 src/sys/netinet/ip_encap.c
Thanks To
=========
Yasuhiro Ohishi for pointing out the problem.
Kengo Nakahara for providing the fix.
More Information
================
Advisories may be updated as new information becomes available.
The most recent version of this advisory (PGP signed) can be found at
https://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2020-002.txt.asc
Information about NetBSD and NetBSD security can be found at
https://www.NetBSD.org/
https://www.NetBSD.org/Security/
Copyright 2020, The NetBSD Foundation, Inc. All Rights Reserved.
Redistribution permitted only in full, unmodified form.
$NetBSD: NetBSD-SA2020-002.txt.asc,v 1.3 2020/03/11 02:33:04 christos Exp $
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