NetBSD Security Advisory 2018-003: Remote DoS in IPsec (IPv6)
13 February, 2018 by security-officer@netbsd.org | netbsd
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NetBSD Security Advisory 2018-003
=================================
Topic: Remote DoS in IPsec (IPv6)
Version: NetBSD-current: source prior to Wed, Jan 24th 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: Wed, Jan 24th 2018
NetBSD-7-1 branch: Mon, Jan 29th 2018
NetBSD-7-0 branch: Mon, Jan 29th 2018
NetBSD-7 branch: Mon, Jan 29th 2018
NetBSD-6-1 branch: Mon, Jan 29th 2018
NetBSD-6-0 branch: Mon, Jan 29th 2018
NetBSD-6 branch: Mon, Jan 29th 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.
Abstract
========
A mistake in the way IPsec parses IPv6-AH packets allowed an attacker to
remotely crash the kernel with a single IPv6 packet.
Technical Details
=================
When receiving an IPv6-AH packet, IPsec must zero out the IPv6 options
that are mutable. To achieve that, it must find the IPPROTO_HOPOPTS and
IPPROTO_DSTOPTS options, and iterate over the suboptions they contain.
A suboption is made of a header and a payload. The header is two-byte-sized:
the second byte indicates the length of the payload, but does not count the
size of the suboption header itself.
A mistake existed in the suboption iteration procedure: the parser's loop
was incremented by the length of the payload, but was not added an
additional two bytes. Therefore, if a suboption had a 'length' field of
zero, the kernel would enter an infinite loop.
By sending a single IPv6-AH packet with a suboption of length zero, an
attacker could remotely make the kernel unresponsive.
Moreover, the suboption parser was written with the assumption that an
incoming IPv6 packet already went through the generic IPv6 parser, and
that therefore several fields were already guaranteed to be valid. Because
of the aforementioned bug, this assumption did not hold anymore, and it was
possible for an attacker to remotely trigger a buffer overflow that would
fill with zeros an area that extends beyond the buffer containing the
packet.
Important Note
==============
Several other issues have been, and are being, identified in the IPsec code.
It is not yet clear whether they are exploitable or not, but the fixes are
being propagated to the Stable branches. Therefore, while a Security
Advisory may not be available shortly, it is recommended that users of IPsec
keep their systems up-to-date.
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
---- ---- -------- ---------- ----------
src/sys/netipsec/xform_ah.c
1.76 1.42.4.1 1.42.8.1 1.42.12.1
FILE netbsd-6 netbsd-6-0 netbsd-6-1
---- -------- ---------- ----------
src/sys/netipsec/xform_ah.c
1.37.2.1 1.37.6.1 1.37.8.1
To update from CVS, re-build, and re-install the kernel:
# cd src
# cvs update -d -P -r VERSION sys/netipsec/xform_ah.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/guide/en/chap-kernel.html
Thanks To
=========
Maxime Villard for finding and fixing the issue.
Revision History
================
2018-02-12 Initial release
More Information
================
Advisories may be updated as new information becomes available.
The most recent version of this advisory (PGP signed) can be found at
http://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2018-0XX.txt.asc
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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