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NetBSD Security Advisory 2018-004
Topic: Remote Memory Corruption in IPv6
Version: NetBSD-current: source prior to Tue, Jan 30th 2018
NetBSD 7.1: affected
NetBSD 7.0 - 7.0.2: affected
NetBSD 6.1 - 6.1.4: affected
NetBSD 6.0 - 6.0.5: affected
Severity: Remote DoS, Remote Memory Corruption
Fixed: NetBSD-current: Tue, Jan 30th 2018
NetBSD-7-1 branch: Tue, Jan 30th 2018
NetBSD-7-0 branch: Tue, Jan 30th 2018
NetBSD-7 branch: Tue, Jan 30th 2018
NetBSD-6-1 branch: Tue, Jan 30th 2018
NetBSD-6-0 branch: Tue, Jan 30th 2018
NetBSD-6 branch: Tue, Jan 30th 2018
Teeny versions released later than the fix date will contain the fix.
Please note that NetBSD releases prior to 6.0 are no longer supported.
It is recommended that all users upgrade to a supported release.
A mistake in the way received IPv6 packets are handled allowed an attacker
to remotely trigger a memory corruption.
When a packet is received, the kernel stores it in memory as chain of mbufs.
An mbuf is basically a block of contiguous memory.
A function, located deep into the IPv6 entry point, was not performing the
necessary checks when treating a received IPv6 packet. It was parsing the
IPv6 options assuming they were located in the first mbuf of the chain, but
this assumption was incorrect. Therefore, it was possible for this function
to return a pointer that pointed to an area located after the first mbuf.
This pointer was then either read from, or written to with one byte that
could be controlled by the packet.
It has been demonstrated that by sending a special combination of nested
IPv6 fragments, this bug could be exploited remotely, and could allow an
attacker to cause the kernel to behave unexpectedly because random areas of
memory were overwritten. It is not clear whether this attack could be turned
to a code execution attack.
The PF firewall can mitigate this particular attack, because it rejects
nested IPv6 fragments by default. NPF does not reject such fragments by
default. The status of IPF in this regard has not been investigated. It is
possible that other vectors than IPv6 fragments could trigger this
Solutions and Workarounds
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 summarize how to upgrade your
kernel. In these instructions, replace:
ARCH with your architecture (from uname -m),
KERNCONF with the name of your kernel configuration file and
VERSION with the file version below
File versions containing the fixes:
FILE HEAD netbsd-7 netbsd-7-0 netbsd-7-1
---- ---- -------- ---------- ----------
1.65 126.96.36.199 188.8.131.52 184.108.40.206
1.187 220.127.116.11 18.104.22.168.2.1 22.214.171.124.6.1
1.78 126.96.36.199 188.8.131.52.2.1 184.108.40.206.6.1
1.160 220.127.116.11 18.104.22.168 22.214.171.124.2.1
FILE netbsd-6 netbsd-6-0 netbsd-6-1
---- -------- ---------- ----------
126.96.36.199 188.8.131.52.4.2 184.108.40.206.2.1
220.127.116.11 18.104.22.168 22.214.171.124
126.96.36.199 188.8.131.52 184.108.40.206
220.127.116.11 18.104.22.168 22.214.171.124
126.96.36.199 188.8.131.52 184.108.40.206
220.127.116.11 18.104.22.168 22.214.171.124
126.96.36.199 188.8.131.52 184.108.40.206
Note: for NetBSD-6, there are three more files that contain the fix.
To update from CVS, re-build, and re-install the kernel:
# cd src
# cvs update -d -P -r VERSION sys/netinet6/frag6.c
# cvs update -d -P -r VERSION sys/netinet6/ip6_input.c
# cvs update -d -P -r VERSION sys/netinet6/ip6_var.h
# cvs update -d -P -r VERSION sys/netinet6/raw_ip6.c
If you run NetBSD-6:
# cvs update -d -P -r VERSION sys/netinet6/ah_input.c
# cvs update -d -P -r VERSION sys/netinet6/esp_input.c
# cvs update -d -P -r VERSION sys/netinet6/ipcomp_input.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:
Maxime Villard for finding and fixing the issue.
2018-02-12 Initial release
Advisories may be updated as new information becomes available.
The most recent version of this advisory (PGP signed) can be found at
Information about NetBSD and NetBSD security can be found at
http://www.NetBSD.org/ and http://www.NetBSD.org/Security/ .
Copyright 2018, The NetBSD Foundation, Inc. All Rights Reserved.
Redistribution permitted only in full, unmodified form.
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