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AUSCERT External Security Bulletin Redistribution
embryonic TCP sockets local DoS
29 November 2013
AusCERT Security Bulletin Summary
Operating System: NetBSD
Impact/Access: Denial of Service -- Existing Account
Revision History: November 29 2013: Specified OS - NetBSD
November 28 2013: Initial Release
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NetBSD Security Advisory 2013-011
Topic: embryonic TCP sockets local DoS
Version: NetBSD-current: source prior to Nov 2nd, 2013
NetBSD 6.1 - 6.1.2: affected
NetBSD 6.0 - 6.0.2: affected
NetBSD 5.1 - 5.1.2: not affected
NetBSD 5.2: not affected
Severity: local DoS
Fixed: NetBSD-current: Nov 2nd, 2013
NetBSD-6-0 branch: Nov 25th, 2013
NetBSD-6-1 branch: Nov 25th, 2013
NetBSD-6 branch: Nov 25th, 2013
Teeny versions released later than the fix date will contain the fix.
Please note that NetBSD releases prior to 5.1 are no longer supported.
It is recommended that all users upgrade to a supported release.
Recently two vulnerabilities in the area of embryonic sockets have been
fixed. Both issues are due to a socket not having credentials set during
a very short timeframe of its creation, and can lead to a user causing
a panic by timing a tcpdrop just right.
The network code adds new connections to the connection table
in an interrupt and references a socket from this table. The
socket is also added to the accept queue of the listening socket.
At this point the socket has no credentials, but tcpdrop can
find it in the connection table and crash the system, for the first
issue by looking up its credentials and hitting an assertion, and in
the second version by referencing a NULL pointer.
Solutions and Workarounds
Install and reboot to a kernel containing the fixes.
The fastest way to do that, if you are running or can run a standard
kernel built as part of the NetBSD release process, is to obtain the
corresponding kernel from the daily NetBSD autobuild output and
install it on your system.
You can obtain such kernels from http://nyftp.netbsd.org/pub/NetBSD-daily/
where they are sorted by NetBSD branch, date, and architecture. To
fix a system running e.g. NetBSD 6.0 or the stable NetBSD 6.0 branch,
the most appropriate kernel will be the "netbsd-6-0" kernel.
To fix a system running NetBSD-current, the "HEAD" kernel should be
used. In all cases, a kernel from an autobuild dated newer than the
fix date for the branch you are using must be used to fix the problem.
If you cannot use the autobuilt kernels, then for all affected 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.
NEWVERSION with the CVS version of the fix
Versions of src/sys/netinet/tcp_usrreq.c:
Versions of src/sys/kern/uipc_socket.c:
To update from CVS, re-build, and re-install the kernel:
# cd src
# cvs update -rNEWVERSION src/sys/netinet/tcp_usrreq.c
# cvs update -rNEWVERSION src/sys/kern/uipc_socket.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:
Thanks to Brian Marcotte for finding the issues and Christos Zoulas and
Michael van Elst for developing fixes.
2013-11-27 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 2013, The NetBSD Foundation, Inc. All Rights Reserved.
Redistribution permitted only in full, unmodified form.
$NetBSD: NetBSD-SA2013-011.txt,v 1.2 2013/11/26 23:59:25 tonnerre Exp $
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