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NetBSD-SA2006-002.txt

NetBSD-SA2006-002.txt
Posted Jan 10, 2006
Site NetBSD.org

NetBSD Security Advisory 2006-002 - The prohibition against setting the system time backwards at securelevel > 1 can be circumvented.

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systems | netbsd
SHA-256 | 33a33c215be8aa045ca247a1c0e1ac47c59ae2bd144cf0a07a66691b4e87e4ae

NetBSD-SA2006-002.txt

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NetBSD Security Advisory 2006-002
=================================

Topic: settimeofday() time wrap

Version: NetBSD-current: source prior to December 5, 2005
NetBSD 3.0: not affected
NetBSD 2.1: affected
NetBSD 2.0.3: affected
NetBSD 1.6.2: affected

Severity: ability to set the time backwards at securelevel > 1

Fixed: NetBSD-current: December 5, 2005
NetBSD-3 branch: December 6, 2005
NetBSD-2.1 branch: December 6, 2005
NetBSD-2.0 branch: December 6, 2005
NetBSD-2 branch: December 6, 2005
NetBSD-1.6 branch: December 6, 2005

Abstract
========

The prohibition against setting the system time "backwards"
at securelevel > 1 can be circumvented.

Technical Details
=================

Setting the time backwards is not regularly allowed at securelevel > 1.
The settime() code in the kernel had no provision against wrapping.
Once the clock reached approximately "Tue Jan 19 03:14:07 UTC 2038",
it will wrap to "Fri Dec 13 20:45:52 UTC 1901". After that, a root
process can set the time to any value, since all values are greater
than that. The fixed version of the code does not allow anyone to
set the time after "Tue Jan 19 03:14:07 UTC 2037" thus one will have
to wait for a year for the time to wrap in order to take advantage
of 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 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 sys/kern/kern_time.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
=========

Markus Vervier from RedTeam Pentesting for reporting the bug
and Christos Zoulas for the fix.


Revision History
================

2006-01-09 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
ftp://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2006-002.txt.asc

Information about NetBSD and NetBSD security can be found at
http://www.NetBSD.org/ and http://www.NetBSD.org/Security/.


Copyright 2006, The NetBSD Foundation, Inc. All Rights Reserved.
Redistribution permitted only in full, unmodified form.

$NetBSD: NetBSD-SA2006-002.txt,v 1.9 2006/01/09 14:48:35 gendalia Exp $

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